FORM 4
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Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person *
Millegan Michael
 2. Issuer Name and Ticker or Trading Symbol
CoreSite Realty Corp [COR] 		5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)
__X__ Director _____ 10% Owner
_____ Officer (give title below) _____ Other (specify below)
(Last)
(First)
(Middle)

C/O CORESITE REALTY CORPORATION, 1001 17TH STREET, SUITE 500		 3. Date of Earliest Transaction (Month/Day/Year)
05/19/2021
(Street)

DENVER, CO 80202
(City)
(State)
(Zip)
4. If Amendment, Date Original Filed(Month/Day/Year)
6. Individual or Joint/Group Filing
(Check applicable line)

__X__ Form Filed by One Reporting Person
_____ Form Filed by More than One Reporting Person

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned

1.Title of Security (Instr. 3)

2. Transaction Date (Month/Day/Year)

2A. Deemed Execution Date, if any (Month/Day/Year)

3. Transaction Code (Instr. 8)

4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5)

5. Amount of Securities Beneficially Owned Following Reported Transaction(s)
(Instr. 3 and 4)

6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)

7. Nature of Indirect Beneficial Ownership (Instr. 4)

Code

V

Amount

(A) or (D)

Price



Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned
(e.g., puts, calls, warrants, options, convertible securities)

1. Title of Derivative Security
(Instr. 3)

2. Conversion or Exercise Price of Derivative Security

3. Transaction Date (Month/Day/Year)

3A. Deemed Execution Date, if any (Month/Day/Year)

4. Transaction Code
(Instr. 8)

5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5)

6. Date Exercisable and Expiration Date (Month/Day/Year)

7. Title and Amount of Securities Underlying Derivative Security (Instr. 3 and 4)

8. Price of Derivative Security (Instr. 5)

9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)

10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4)

11. Nature of Indirect Beneficial Ownership (Instr. 4)

Code

V

(A)

(D)

Date Exercisable

Expiration Date

Title

Amount or Number of Shares

Restricted Stock Units

 (1) 05/19/2021 A 1,471   (2)   (3)

Common Stock

1,471 $ 0 1,845D 

Explanation of Responses:
1.

Each Restricted Stock Unit ("RSU") represents the right to receive one share of common stock of the issuer. The reporting person also holds a tandem dividend equivalent for each RSU held, which gives the reporting person the right to receive, upon the payment of any ordinary quarterly cash dividend paid to holders of common stock of the issuer, an equivalent payment in the form of additional RSUs based on the fair market value of the issuer's common stock on the date of payment.

2.

The RSUs vest on the earlier of (a) May 19, 2022 or (b) the day before the issuer's next annual meeting of stockholders. In addition, pursuant to a deferral election made by the reporting person, the RSUs are payable upon the earliest of (i) the reporting person's separation from service with the issuer, (ii) the reporting person's death or (iii) the date of a change in control of the issuer.

3.

The RSUs have no expiration date.



Signatures

/s/ Derek S. McCandless, Attorney-in-Fact

05/20/2021
** Signature of Reporting PersonDate
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
* If the form is filed by more than one reporting person, see Instruction 4 (b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
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