FORM 4 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 OF SECURITIES 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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(Print or Type Responses)

1. Name and Address of Reporting Person * MADISON DEARBORN PARTNERS LLC   2. Issuer Name and Ticker or Trading Symbol PACKAGING CORP OF AMERICA [PKG] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director __X__ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) THREE FIRST NATIOANL PLAZA STE 3800,  3. Date of Earliest Transaction (Month/Day/Year) 12/21/2005 (Street) CHICAGO, IL 60602 4. If Amendment, Date Original Filed(Month/Day/Year) 6. Individual or Joint/Group Filing(Check Applicable Line) ___ Form filed by One Reporting Person _X_ Form filed by More than One Reporting Person (City) (State) (Zip) 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 Common Stock 12/21/2005   S   17,825,000 (1) D $ 20.69 26,273,010 I Through PCA Holdings LLC (2) Common Stock 12/21/2005   S   4,500,000 (3) D $ 20.69 21,773,010 I Through PCA Holdings LLC (2)

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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 Underlying Securities (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

Reporting Owners

Reporting Owner Name / Address	Relationships
	Director	10% Owner	Officer	Other
MADISON DEARBORN PARTNERS LLC THREE FIRST NATIOANL PLAZA STE 3800 CHICAGO, IL 60602		X
MADISON DEARBORN PARTNERS III LP THREE FIRST NATIONAL PLAZA STE 3800 CHICAGO, IL 60602		X
MADISON DEARBORN CAPITAL PARTNERS III LP THREE FIRST NATIONAL PLAZA SUITE 3800 CHICAGO, IL 60602		X

Signatures

/s/ Madison Dearborn Partners, LLC, by Samuel M. Mencoff, its Managing Director		12/22/2005
**Signature of Reporting Person		Date

Explanation of Responses:

*	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).
(1)	Represents shares sold by PCA Holdings LLC in an underwritten offering pursuant to a registration statement filed by the issuer on December 9, 2005.
(2)	The reported securities are owned directly by PCA Holdings LLC ("Holdings"). The members of Holdings are Madison Dearborn Capital Partners III, L.P. ("MDCP III") and a fund affiliated with MDCP III. MDCP III and its affiliated fund may be deemed to have beneficial ownership of the securities owned by Holdings. The securities beneficially owned by MDCP III and its affiliated fund may be deemed to be beneficially owned by Madison Dearborn Partners III, L.P. ("MDP III"), the general partner of MDCP III and its affiliated fund, and by Madison Dearborn Partners, LLC, the general partner of MDP III. Each of the reporting persons disclaims beneficial ownership of these shares except to the extent of such reporting person's pecuniary interest therein, and the inclusion of these shares in this report shall not be deemed an admission of beneficial ownership of the reported shares for purposes of Section 16 or for any other purpose.
(3)	Represents shares repurchased by the issuer from PCA Holdings LLC at a price per share equal to the net price per share received by PCA Holdings LLC in the underwritten offering.

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