X0306 4 2015-08-18 0 0001402057 CDW Corp CDW 0001181100 MADISON DEARBORN PARTNERS LLC C/O MADISON DEARBORN PARTNERS, LLC 70 W. MADISON STREET, SUITE 4600 CHICAGO IL 60602 0 0 1 0 0001344692 Madison Dearborn Capital Partners V - A L P C/O MADISON DEARBORN PARTNERS, LLC 70 W. MADISON STREET, SUITE 4600 CHICAGO IL 60602 0 0 1 0 0001344693 Madison Dearborn Capital Partners V - C L P C/O MADISON DEARBORN PARTNERS, LLC 70 W. MADISON STREET, SUITE 4600 CHICAGO IL 60602 0 0 1 0 0001362213 MADISON DEARBORN CAPITAL PARTNERS V EXECUTIVE-A L P C/O MADISON DEARBORN PARTNERS, LLC 70 W. MADISON STREET, SUITE 4600 CHICAGO IL 60602 0 0 1 0 0001416217 MDCP Co-Investors (CDW) LP C/O MADISON DEARBORN PARTNERS, LLC 70 W. MADISON STREET, SUITE 4600 CHICAGO IL 60602 0 0 1 0 0001579972 MADISON DEARBORN PARTNERS V-A&C, L.P. C/O MADISON DEARBORN PARTNERS, LLC 70 W. MADISON STREET, SUITE 4600 CHICAGO IL 60602 0 0 1 0 0001219630 MENCOFF SAMUEL M C/O MADISON DEARBORN PARTNERS, LLC 70 W. MADISON STREET, SUITE 4600 CHICAGO IL 60602 0 0 1 0 Common Stock, par value $0.01 2015-08-18 4 S 0 6550571 38.25 D 13104898 I See footnotes Consists of 4,275,998 shares sold by Madison Dearborn Capital Partners V-A, L.P. ("MDP A"), 1,134,348 shares sold by Madison Dearborn Capital Partners V-C, L.P. ("MDP C"), 42,966 shares sold by Madison Dearborn Capital Partners V Executive-A, L.P. ("MDP Exec") and 1,097,259 shares sold by MDCP Co-Investor (CDW), L.P. ("MDP Co-Investor") in an underwritten secondary offering. This sale price reflects the public offering price. The price received by the reporting persons will be reduced by the underwriters' commission of $0.25 per share. Consists of 8,554,448 shares held directly by MDP A, 2,269,348 shares held directly by MDP C, 85,955 shares held directly by MDP Exec and 2,195,147 shares held directly by MDCP Co-Investor. MDP V is the general partner of MDP A, MDP C, MDP Exec and MDP Co-Investor. MDP is the general partner of MDP V. As the sole members of a limited partner committee of MDP V that has the power, acting by majority vote, to vote or dispose of the shares directly held by MDP A, MDP C, MDP Exec and MDP Co-Investor, Paul J. Finnegan and Samuel M. Mencoff may be deemed to have shared voting and investment power over such shares. Each of Messrs. Finnegan and Mencoff and MDP V hereby disclaims any beneficial ownership of any shares held by MDP A, MDP C, MDP Exec and MDP Co-Investor except to the extent of its or his pecuniary interest therein. Mr. Mencoff has an indirect pecuniary interest in the shares of CDW Corporation's common stock held of record by the various MDP funds described above through his investment in MDP V. Each of MDP A, MDP C, MDP Exec and MDP Co-Investor and Mr. Mencoff may be deemed to share beneficial ownership of the reported securities and expressly disclaims beneficial ownership of such shares except to the extent of its or his pecuniary interest therein. Mr. Finnegan has separately filed a Form 4. Madison Dearborn Partners LLC by /s/ James S. Rowe, under Power of Attorney 2015-08-20 Madison Dearborn Capital Partners V-A, L.P. by /s/ James S. Rowe, under Power of Attorney 2015-08-20 Madison Dearborn Capital Partners V-C, L.P. by /s/ James S. Rowe, under Power of Attorney 2015-08-20 Madison Dearborn Capital Partners V Executive-A, L.P. by /s/ James S. Rowe, under Power of Attorney 2015-08-20 MDCP Co-Investors (CDW), L.P. by /s/ James S. Rowe, under Power of Attorney 2015-08-20 Madison Dearborn Partners V - A&C, L.P. by /s/ James S. Rowe, under Power of Attorney 2015-08-20 Samuel M. Mencoff by /s/ James S. Rowe, under Power of Attorney 2015-08-20