ZAYO Zayo Group Holdings Inc

Item 1. Security and Issuer.

This Schedule 13D (the “Schedule”) relates to the common stock, par value $0.001 per share (“Shares”), of Zayo Group Holdings, Inc., a Delaware corporation (the “Issuer”).

The principal executive offices of the Issuer are located at 1821 30th Street, Unit A, Boulder, CO 80301.

Item 2. Identity and Background.

This Schedule is being filed by BlackRock, Inc. (“BlackRock”). BlackRock is a Delaware corporation that, through its subsidiaries, provides diversified investment management directly and indirectly through various investment products to institutions, intermediaries and individual investors. Investment management services primarily consist of the management of equity, fixed income, multi-asset class, alternative investment and cash management products. BlackRock, through its subsidiaries, offers its investment products in a variety of accounts, including open-end and closed-end mutual funds, iShares® exchange-traded funds, collective investment trusts and separate accounts. In addition, BlackRock, through its subsidiaries, provides market risk management, financial markets advisory and enterprise investment system services to a broad base of clients. Financial markets advisory services include valuation services relating to illiquid securities, dispositions and workout assignments (including long-term portfolio liquidation assignments), risk management and strategic planning and execution. The principal office and business address of BlackRock is 55 East 52nd Street, New York, NY 10055.

Certain of the securities reported herein were previously included in a statement on Schedule 13G filed by BlackRock on February 8, 2019. BlackRock did not acquire any beneficial ownership of Shares with the purpose or effect of changing or influencing the control of the Issuer or as a participant in any transaction having such purpose or effect, or in connection with any plan or proposal that would be subject to disclosure under Item 4 of the Schedule with respect to the Issuer. BlackRock subsidiaries, as the investment advisers to certain client accounts, hold Shares in their ordinary course of business, not with the purpose or effect of changing or influencing the control of the Issuer or as a participant in any transaction having such purpose or effect, and not in connection with any plan or proposal that would be subject to disclosure under Item 4 of the Schedule with respect to the Issuer. Therefore, BlackRock does not believe that it is required to file the Schedule pursuant to Rule 13d-1 under the Act, however, BlackRock is voluntarily filing this Schedule because certain of its other affiliates entered into the transactions described in Item 4 below.

(a) – (c) and (f) Current information concerning the identity and background of each of the executive officers and directors of BlackRock is set forth on Annex A (collectively, the “Covered Persons”), attached hereto and incorporated herein by reference.

(d) and (e)

During the last five years, none of BlackRock or, to the best of its knowledge, any of the Covered Persons has (i) been convicted in any criminal proceeding (excluding traffic violations or similar misdemeanors) or (ii) except as set forth on Annex B , attached hereto, has been a party to a civil proceeding of any judicial or administrative body of competent jurisdiction as a result of which such person was or is subject to a judgment, decree or final order enjoining future violations of, or prohibiting or mandating activities subject to, federal or state securities laws or finding of any violation with respect to such laws.

Neither the present filing nor anything contained herein shall be construed as an admission that BlackRock constitutes a “person” for any purposes other than Section 13(d) of the Act.

Item 3. Source and Amount of Funds or Other Consideration.

As of May 15, 2019, BlackRock, in its role as the ultimate parent of investment advisers to certain client accounts, held beneficial ownership of 12,140,295 Shares acquired prior to such date for an aggregate purchase price of $378,088,272.88. Such acquisitions were made for investment purposes with available funds of the applicable client accounts in the ordinary course of business of BlackRock’s investment adviser subsidiaries.

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Item 4. Purpose of Transaction.

All of the Shares of the Issuer were acquired for investment purposes by funds and accounts for which certain of BlackRock’s subsidiaries act as investment advisers.

On May 8, 2019, certain funds managed by subsidiaries of BlackRock entered into subscription documents (the “Subscription Agreements”) for the purchase of limited partnership interests in DC Front Range Holdings I, LP, a Delaware limited partnership (“DC Front Range”). Pursuant to the Subscription Agreements, such funds managed by subsidiaries of BlackRock agreed to contribute in the aggregate approximately $96.6 million to DC Front Range at the effective time (the “Effective Time”) of the Merger (as defined below) to fund the transactions contemplated by the Agreement and Plan of Merger (the “Merger Agreement”) dated May 8, 2019 by and the Issuer, Front Range TopCo, Inc. (“Parent”), a Delaware corporation, and Front Range BidCo, Inc., a Delaware corporation and wholly owned subsidiary of Parent (“Merger Sub”), providing for the merger of Merger Sub with and into the Issuer (the “Merger”), with the Issuer surviving the Merger as a wholly owned subsidiary of Parent. DC Front Range is an investment vehicle sponsored by Digital Colony GP, LLC, which is a joint venture between Colony Capital Operating Company, LLC (“CCOC”), an entity managed by Colony Capital, Inc. (“Colony Capital”), and Digital Bridge Holdings, LLC. As a result, BlackRock may be deemed to have formed a “group,” as such term is used in Regulation 13D under the Act with Colony Capital and CCOC. BlackRock disclaims any membership or participation in a “group” with Colony Capital and/or its affiliates and further disclaims beneficial ownership of any Shares beneficially owned by Colony Capital and/or its affiliates, including 25,000 Shares believed to be beneficially owned by Colony Capital and/or its affiliates on the date hereof.

Pursuant to the Merger Agreement, at the Effective Time, each Share that is outstanding immediately prior to such time (other than (i) Shares owned by Parent, Merger Sub, the Issuer (including any Shares held in the treasury of the Issuer) or by any direct or indirect wholly owned subsidiary of Parent, Merger Sub or the Issuer, or (ii) Shares held by stockholders of the Issuer who have not voted in favor of the Merger (and who are entitled to demand and properly demand their statutory rights of appraisal in accordance with the Delaware General Corporation Law) will be cancelled and extinguished and automatically converted into the right to receive cash in an amount equal to $35.00 per share without interest. Consummation of the Merger is subject to certain customary closing conditions, including, without limitation, obtaining the required Company stockholder approval, the absence of certain legal impediments, the expiration or termination of the required waiting periods under the Hart-Scott-Rodino Antitrust Improvements Act of 1976, as amended, review and clearance by the Committee on Foreign Investment in the United States, certain foreign antitrust regulatory approvals and certain other filings and approvals.

The foregoing description of the Subscription Agreements does not purport to be complete and is qualified in its entirety by reference to the full text of such agreement filed as an exhibit to this Schedule, and incorporated herein by reference.

The entry into the Subscription Agreements by certain funds managed by subsidiaries of BlackRock, none of which own Shares, will not restrict BlackRock’s subsidiaries’ exercise of investment or voting power with respect to the Shares to which this Schedule relates.

Except as set forth in this Schedule, BlackRock has no present plans or proposals that relate to or would result in any of the actions described in Item 4(a) through (j) of the Schedule. Each of BlackRock’s advisory subsidiaries may evaluate on a continuing basis its client accounts’ investment in the Issuer and BlackRock expects that such subsidiaries may from time to time acquire or dispose of Shares or other securities of the Issuer on behalf of such client accounts. Any acquisitions or dispositions will depend upon (i) the price and availability of the Issuer’s securities; (ii) subsequent developments concerning the Issuer’s business and prospects and the industry in which the Issuer operates; (iii) BlackRock’s advisory subsidiaries’ general investment policies with respect to the applicable accounts managed by BlackRock’s advisory subsidiaries; (iv) other investment and business opportunities available to BlackRock’s advisory subsidiaries on behalf of their clients; (v) general market and economic conditions; (vi) tax considerations; and (vii) such other factors as BlackRock’s advisory subsidiaries may consider relevant. Any such acquisitions or dispositions may be made, subject to applicable law, in open market transactions or privately negotiated transactions.

Item 5. Interest in Securities of the Issuer.

(a) and (b) The responses of BlackRock to Rows (7) through (11) of the cover page of this Schedule are incorporated herein by reference. In addition, pursuant to Section 13(d)(3) of the Act, BlackRock and Colony Capital and/or its affiliates may on the basis of the facts described elsewhere herein be considered to be a “group.” BlackRock disclaims any

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membership or participation in a “group” with Colony Capital and/or its affiliates and further disclaims beneficial ownership of any Shares beneficially owned by Colony Capital and/or its affiliates, including 25,000 Shares believed to be beneficially owned by Colony Capital and/or its affiliates on the date hereof.

The Shares beneficially owned by BlackRock include Shares beneficially owned by its subsidiaries, including BlackRock (Luxembourg) S.A., BlackRock Advisors (UK) Limited, BlackRock Advisors, LLC, BlackRock Asset Management Canada Limited, BlackRock Asset Management Ireland Limited, BlackRock Financial Management, Inc., BlackRock Fund Advisors, BlackRock Institutional Trust Company, National Association, BlackRock International Limited, BlackRock Investment Management (UK) Limited, and BlackRock Investment Management, LLC, none of which beneficially owns in excess of 5% of the outstanding Shares.

Except as set forth herein, neither BlackRock nor, to the knowledge of BlackRock, the Covered Persons beneficially own any Shares as of May 15, 2019.

(c) Annex C , attached hereto, sets forth transactions in the Shares that were effected during the 60-day period ended May 15, 2019. The transactions in the Shares described on Annex C were effected on securities exchanges unless otherwise indicated therein.

Except as set forth in this Schedule, neither BlackRock nor, to the best of its knowledge, any of the Covered Persons has engaged in any transaction in any Shares during the 60-day period ended May 15, 2019.

(d) Except for investment advisory clients of BlackRock’s subsidiaries, who may have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, Shares, no other person is known by BlackRock to have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, any Shares that may be beneficially owned by BlackRock.

(e) Not applicable.

Item 6. Contracts, Arrangements, Understandings or Relationships with Respect to Securities of the Issuer.

The information set forth in Item 4 is hereby incorporated herein by reference.

Except as set forth in this Schedule, there are no contracts, arrangements, understandings or relationships between BlackRock and any other person with respect to any securities of the Issuer or among the investment advisory subsidiaries of BlackRock, including but not limited to transfer or voting of any securities of the Issuer, finder’s fees, joint ventures, loan or option arrangements, puts or calls, guarantees of profits, division of profits or loss, or the giving or withholding of proxies (other than the transfer of voting rights with respect to Shares that are loaned out in the ordinary course of BlackRock’s and its subsidiaries’ securities lending programs).

Item 7. Materials to Be Filed as Exhibits.

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SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Date: May 17, 2019

Annex A

The following is a list of the executive officers and directors of BlackRock, Inc. (collectively, the “Covered Persons”), setting forth the present principal occupation or employment and the name, principal business and address of any corporation or other organization in which such employment is conducted and citizenship for each such person. Each Covered Person is a citizen of the United States, unless otherwise noted, and does not have any other principal occupation (outside of similar positions held with respect to other entities directly or indirectly managed or advised by BlackRock).

Executive Officers

A-1

Directors

A-2

A-3

Annex B

On January 17, 2017, BlackRock reached an agreement with the U.S. Securities and Exchange Commission (the “SEC”), resolving a matter regarding a provision in an old version of BlackRock’s form employee separation agreement that the SEC found violated the Dodd Frank Act’s whistleblower provisions. In the settlement with the SEC, BlackRock agreed to pay a $340,000 penalty and consented to the entry of an Administrative Order containing a finding that BlackRock violated Rule 21F-17 under the Act and ordering BlackRock to cease and desist from committing or causing any violations and any future violations of Rule 21F-17.

B-1

Annex C

Transactions in Shares

(60-day period ended on May 15, 2019)

C-1

C-2

C-3

C-4

C-5

C-6

C-7

C-8

C-9

C-10