Class Investor I Y PORTFOLIO TURNOVER Ticker DHRAX DHRIX DHRYX The fund pays transaction costs, such as commissions, when it Before you invest, you may want to review the fund’s Prospectus, which buys and sells securities (or “turns over” its portfolio). A higher contains information about the fund and its risks. The fund’s Prospectus and portfolio turnover rate may indicate higher transaction costs and Statement of Additional Information, both dated February 28, 2021, are may result in higher taxes when fund shares are held in a taxable incorporated by reference into this Summary Prospectus. For free paper or account. These costs, which are not reflected in annual fund electronic copies of the fund’s Prospectus and other information about the operating expenses or in the Example, affect the fund’s fund, go to http://www.diamond-hill.com/mutual-funds/documents.fs, email a performance. During the most recent fiscal year, the fund’s request to [email protected], call 888-226-5595, or ask any financial portfolio turnover rate was 28% of the average value of advisor, bank, or broker-dealer who offers shares of the fund. its portfolio. Investment Objective Principal Investment Strategy The investment objective of the Diamond Hill Core Fund is to maximize total return consistent with the preservation of Under normal market conditions, the fund intends to provide capital. total return by investing at least 80% of its net assets (plus any amounts borrowed for investment purposes) in a diversified Fees and Expenses of the Fund portfolio of investment grade, securities, including This table describes the fees and expenses that you may pay if bonds, debt securities and other similar U.S. dollar- you buy and hold shares of the fund. You may pay other fees, denominated instruments issued by various U.S. public- or such as brokerage commissions and other fees to financial private-sector entities, by non-U.S. corporations or U.S. affiliates intermediaries, which are not reflected in the tables and of non-U.S. corporations, including those in emerging markets. examples below. The fund may invest a significant portion or all of its assets in mortgage-related and mortgage-backed securities at the SHAREHOLDER FEES (fees paid directly from your investment) discretion of Diamond Hill Capital Management, Inc. (the “Adviser”). None Under normal circumstances, the fund will maintain an average ANNUAL FUND OPERATING EXPENSES (expenses that you portfolio duration of plus or minus 20% of the duration of the pay each year as a percentage of the value of your investment) Bloomberg Barclays U.S. Aggregate Bond Index. The Bloomberg Investor Class I Class Y Barclays US Aggregate Bond Index is a broad-based index that Management fees 0.30% 0.30% 0.30% represents the investment grade, US dollar-denominated fixed- rate taxable . Duration of the Bloomberg Barclays Distribution (12b-1) fees 0.25% None None US Aggregate Bond Index was 5.86 as of its last reconstitution Other expenses 0.21% 0.17% 0.05% date of January 31, 2021. Duration is an approximate measure of Total annual fund operating expenses 0.76% 0.47% 0.35% a bond’s price sensitivity to changes in interest rates. For instance, a duration of “three” means that a ’s or EXPENSE EXAMPLE portfolio’s price would be expected to decrease by approximately 3% with a 1% increase in interest rates (assuming This Example is intended to help you compare the cost of a parallel shift in ). investing in the fund with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the fund In selecting securities for the fund, the Adviser performs a risk/ for the time periods indicated and then redeem all of your shares reward analysis that includes an evaluation of credit risk, at the end of those periods. The Example also assumes that your interest rate risk, prepayment risk, and the legal and technical investment has a 5% return each year and that the fund’s structure of the security. The Adviser will attempt to take operating expenses remain the same. Although your actual costs advantage of inefficiencies that it believes exist in the fixed- may be higher or lower, based on these assumptions your costs income markets. The Adviser seeks to invest in securities that would be: the Adviser expects to offer attractive prospects for current income and/or capital appreciation in relation to the risk borne. 1 Year 3 Years 5 Years 10 Years Investor $78 $243 $422 $942 Main Risks Class I 48 151 263 591 All investments carry a certain amount of risk and the fund Class Y 36 113 197 443 cannot guarantee that it will achieve its investment objective. An investment in the fund is not a deposit or obligation of any bank, is not endorsed or guaranteed by any bank, and is not insured by the Federal Deposit Insurance Corporation (FDIC) or any other government agency. You may lose money by investing in the fund. Below are the main risks of investing in the fund. All

DIAMOND HILL FUNDS | SUMMARY PROSPECTUS | FEBRUARY 28, 2021| DIAMOND-HILL.COM Core Summary February 28, 2021 of the risks listed below are significant to the fund, regardless of impact the sale price. Transactions involving bank loans may the order in which they appear. have significantly longer periods than more Asset-Backed, Mortgage-Related and Mortgage-Backed traditional investments (settlement can take longer than 7 days) and often involve borrowers whose financial condition is Securities Risk The fund may invest in asset-backed, troubled or highly leveraged, which increases the risk that the mortgage-related and mortgage-backed securities, including so- fund may not receive its proceeds in a timely manner or that the called “sub-prime” mortgages that are subject to certain other fund may incur losses in order to pay redemption proceeds to its risks including prepayment and call risks. When mortgages and shareholders. In addition, loans are not registered under the other obligations are prepaid and when securities are called, the federal securities laws like and bonds, so investors in fund may have to reinvest in securities with a lower yield or fail loans have less protection against improper practices than to recover additional amounts (i.e., premiums) paid for investors in registered securities. securities with higher interest rates, resulting in an unexpected capital loss and/or a decrease in the amount of dividends and Credit Risk There is a risk that issuers and counterparties will yield. In periods of rising interest rates, the fund may be subject not make payments on securities and repurchase agreements to extension risk, and may receive principal later than expected. held by a fund. Such default could result in losses to the fund. In As a result, in periods of rising interest rates, the fund may addition, the credit quality of securities held by the fund may be exhibit additional volatility. During periods of difficult or frozen lowered if an issuer’s financial condition changes. Lower credit credit markets, significant changes in interest rates, or quality may lead to greater volatility in the price of a security and deteriorating economic conditions, such securities may decline in shares of the fund. Lower credit quality also may affect in value, face valuation difficulties, become more volatile and/or liquidity and make it difficult for the fund to sell the security. become illiquid. Fixed Income Risk The fund invests in fixed income securities. Collateralized mortgage obligations (“CMOs”) and stripped These securities will increase or decrease in value based on mortgage-backed securities, including those structured as changes in interest rates. If rates increase, the value of the fund’s interest only (“IOs”) and principal only (“POs”), are more fixed income securities generally declines. On the other hand, if volatile and may be more sensitive to the rate of prepayments rates fall, the value of the fixed income securities generally than other mortgage-related securities. CMOs are issued in increases. Your investment will decline in value if the value of multiple classes, and each class may have its own interest rate the fund’s investments decreases. and/or final payment date. A class with an earlier final payment date may have certain preferences in receiving principal Government Securities Risk The fund may invest in payments or earning interest. As a result, the value of some securities issued or guaranteed by the U.S. government or its classes in which the fund invests may be more volatile and may agencies and instrumentalities. These securities may be backed be subject to higher risk of non-payment. The risk of default, as by the credit of the government as a whole or only by the issuing described under “Credit Risk”, for “sub-prime” mortgages is agency. U.S. Treasury bonds, notes, and bills and some agency generally higher than other types of mortgage-backed securities. securities, such as those issued by the Federal Housing The structure of some of these securities may be complex and Administration and Ginnie Mae, are backed by the full faith and there may be less available information than other types of debt credit of the U.S. government as to payment of principal and securities. interest and are the highest quality government securities. Other The values of IO and PO mortgage-backed securities are more securities issued by U.S. government agencies or volatile than other types of mortgage-related securities. They are instrumentalities, such as securities issued by the Federal Home very sensitive not only to changes in interest rates, but also to the Loan Banks and Freddie Mac, are supported only by the credit of rate of prepayments. A rapid or unexpected increase in the agency that issued them, and not by the U.S. government. prepayments can significantly depress the price of interest-only Securities issued by the Federal Farm Credit System, the Federal securities, while a rapid or unexpected decrease could have the Land Banks, and Fannie Mae are supported by the agency’s right same effect on principal-only securities. In addition, because to borrow money from the U.S. Treasury under certain there may be a drop in trading volume, an inability to find a circumstances, but are not backed by the full faith and credit of ready buyer, or the imposition of legal restrictions on the resale the U.S. government. No assurance can be given that the of securities, these instruments may be illiquid. The fund will be U.S. government would provide financial support to its agencies exposed to additional risk to the extent that it uses inverse and instrumentalities if not required to do so by law. floaters and inverse IOs, which are debt securities with interest rates that reset in the opposite direction from the market rate to Inflation Risk Because inflation reduces the purchasing power which the security is indexed. These securities are more volatile of income produced by existing fixed income securities, the and more sensitive to interest rate changes than other types of prices at which fixed income securities trade will be reduced to debt securities. If interest rates move in a manner not compensate for the fact that the income they produce is worth anticipated by the Adviser, the fund could lose all or less. This potential decrease in market value would be the substantially all of its investment in inverse IOs. measure of the inflation risk incurred by the fund. Consumer Loans Risk Investments in consumer loans expose LIBOR Risk Instruments in which the fund invests may pay the fund to additional risks beyond those normally associated interest at floating rates based on the London Interbank Offered with more traditional debt instruments. The fund’s ability to Rate (“LIBOR”) or may be subject to interest caps or floors based receive payments in connection with the loan depends primarily on LIBOR. In July 2017, the United Kingdom’s Financial Conduct on the financial condition of the borrower and whether or not a Authority announced the desire to phase out the use of LIBOR loan is secured by collateral, although there is no assurance that by the end of 2021. There is currently no definitive information the collateral securing a loan will be sufficient to satisfy the loan regarding the future utilization of LIBOR or of any particular obligation. In addition, bank loans often have contractual replacement rate. Abandonment of or modifications to LIBOR restrictions on resale, which can delay the sale and adversely could have adverse impacts on newly issued financial instruments and existing financial instruments which reference

DIAMOND HILL FUNDS | SUMMARY PROSPECTUS | FEBRUARY 28, 2021| DIAMOND-HILL.COM Core Bond Fund Summary February 28, 2021

LIBOR. Abandonment of or modifications to LIBOR could lead year to year. The table shows the fund’s average annual total to significant -term and long-term uncertainty and market returns for certain time periods compared to the returns of a instability. broad-based securities index. The bar chart and table provide some indication of the risks of investing in the fund. Of course, Management Risk The Adviser’s judgments about the the fund’s past performance is not necessarily an indication of attractiveness, value and potential appreciation of a particular its future performance. Updated performance information is asset class or individual security in which the fund invests may available at no cost by visiting www.diamond-hill.com or by prove to be incorrect and there is no guarantee that individual calling 888-226-5595. investments will perform as anticipated. Market Risk The value of the fund's investments may decrease, CLASS I ANNUAL TOTAL RETURN-YEARS ENDED 12/31 sometimes rapidly or unexpectedly, due to factors affecting an 10% issuer held by the fund, particular industries or overall securities markets. When the value of the fund’s investments goes down, 7.93 7.94 your investment in the fund decreases in value. A variety of factors including interest rate levels, recessions, inflation, U.S. economic growth, war or acts of terrorism, natural disasters, political events and widespread public health issues affect the 5% securities markets. The global spread of novel coronavirus 4.17 disease (COVID-19) was declared a pandemic by the World Health Organization. COVID-19 has caused volatility, severe market dislocations and liquidity constraints in many markets, 1.59 including markets for the securities the fund holds, and may adversely affect the fund's investments and operations. In 0% addition, COVID-19 and governmental responses to COVID-19 2017 2018 2019 2020 may negatively impact the capabilities of the fund's service providers and disrupt the fund's operations. This pandemic may result in substantial market volatility and may adversely impact Best Quarter: 2Q 2020, +4.10% the prices and liquidity of the fund's investments. Worst Quarter: 1Q 2018, -0.84% Non-U.S. and Emerging Markets Risk The fund may invest in non-U.S. securities and U.S. securities of companies AVERAGE ANNUAL TOTAL RETURNS AS OF 12/31/20 domiciled in non-U.S. countries that may experience more rapid The fund’s Investor shares (formerly Class A) were subject to a and extreme changes in value than a fund that invests maximum applicable sales charge of 3.50% which was charged exclusively in securities of U.S. companies. These companies until February 26, 2021, as applicable. This sales charge is not may be subject to additional risks, including political and reflected in the average annual total returns shown below. After- economic risks, civil conflicts and war, greater volatility, tax returns are calculated using the highest historical individual expropriation and nationalization risks, currency fluctuations, federal marginal income tax rate and do not reflect the impact of higher transaction costs, delayed settlement, possible non-U.S. state and local taxes. Actual after-tax returns depend on a controls on investments, and less stringent investor protection shareholders's tax situation and may differ from those shown. and disclosure standards of non-U.S. markets. The departure of After-tax returns are not relevant for shareholders who hold one or more other countries from the European Union may have fund shares in tax-deferred accounts or to shares held by non- significant political and financial consequences for global taxable entities. After-tax returns are shown for Class I shares markets. These risks are magnified in emerging markets as only and will vary from the after-tax returns for the other events and evolving conditions in certain economies or markets classes. may alter the risks associated with investments tied to countries or regions that historically were perceived as comparatively Inception Since Date of Class One Year Inception stable becoming riskier and more volatile. The market for the Class I Before Taxes 07/05/16 7.94% 4.27% securities of issuers in emerging markets is typically small and low, and nonexistent trading volumes in those securities may After Taxes on Distributions 6.89 3.15 result in a lack of liquidity and price volatility. After Taxes on Distributions and Sale of Fund Shares 4.68 2.77 Prepayment and Call Risk The issuer of certain securities Investor Before Taxes 07/05/16 7.60 3.96 may repay principal in advance, especially when yields fall. Class Y Before Taxes 07/05/16 8.04 4.38 Changes in the rate at which prepayments occur can affect the Bloomberg Barclays U.S. Aggregate return on investment of these securities. When debt obligations Index 7.51 3.59 are prepaid or when securities are called, the fund may have to reinvest in securities with a lower yield. The fund also may fail to The Bloomberg Barclays U.S. Aggregate Index is an unmanaged index recover additional amounts (i.e., premiums) paid for securities measuring the performance of the U.S. investment grade fixed rate bond with higher coupons, resulting in an unexpected capital loss. market, with index components for government and corporate securities, mortgage pass through, and asset-backed securities. Performance You cannot invest directly in an index. Unlike mutual funds, an index does not incur expenses. If expenses were deducted, the actual returns of an The following bar chart and table show two aspects of the fund: index would be lower. volatility and performance. The bar chart shows the volatility — or variability — of the fund’s annual total returns over time, and shows that fund performance can change from

DIAMOND HILL FUNDS | SUMMARY PROSPECTUS | FEBRUARY 28, 2021| DIAMOND-HILL.COM Core Bond Fund Summary February 28, 2021

Portfolio Management Dividends, Capital Gains and Taxes Investment Adviser The fund’s distributions may be taxable as ordinary income or Diamond Hill Capital Management, Inc. capital gains, except when your investment is in an IRA, 401(k) or other tax-advantaged investment plan. However, you may be Portfolio Managers subject to tax when you withdraw monies from a tax-advantaged Henry Song plan. Portfolio Manager since 7/2016 Payments to Broker-Dealers and Other Financial Mark Jackson Intermediaries Portfolio Manager If you purchase shares (other than Class Y shares) through a since 7/2016 broker-dealer or other financial intermediary (such as a bank), the fund and its related companies may pay the intermediary for Buying and Selling Fund Shares the sale of fund shares and related services. These payments may create a conflict of interest by influencing the broker-dealer Minimum Initial Investment or other intermediary and your salesperson to recommend the Investor and Class I: $2,500 fund over another investment. Ask your salesperson or visit your Class Y: $500,000 financial intermediary’s web site for more information. To Place Orders Mail: Diamond Hill Core Bond Fund P.O. Box 46707 Cincinnati, OH 45246 Phone: 888-226-5595 Transaction Policies In general, you can buy or sell (redeem) shares of the fund by mail or phone on any business day. You can generally pay for shares by check or wire. You may be charged wire fees or other transaction fees; ask your financial professional. When selling shares, you will receive a check, unless you request a wire. You may also buy and sell shares through a financial professional.

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DIAMOND HILL FUNDS | SUMMARY PROSPECTUS | FEBRUARY 28, 2021| DIAMOND-HILL.COM