CBS' Philadelphia stations include KYW (news), WIP (sports), WPHT (conservative talk), WXTU (country), WOGL ("classic hits") and WTDY (Top 40).
This deal comes months after CBS announced that it would sell or spin off its radio business in 2017, according to the Philadelphia Business Journal.
Entercom was previously the fourth-largest radio station owner with 127 stations in 27 markets.
A purchase price was not disclosed, but the companies said the deal would be structured as a Reverse Morris Trust, which would be tax-free to CBS and its stockholders.
CBS president Les Moonves said previous year that the company was looking for a buyer for its radio division, as it the radio industry continued to struggle with weak advertising sales.
The deal, subject to regulatory approvals and a vote by Entercom's board, is expected to close in the second half of the year.
"This transformational transaction creates scale-driven efficiencies and opportunities to compete more effectively with other media to better serve our listeners and our advertisers", said David J. Field, Entercom president-CEO. Operating under the Entercom brand, the combined company will have 244 stations, including four in Baltimore.
The companies said they posted pro forma adjusted earnings before interest, taxes, depreciation and amortization, or Ebitda, of almost $500 million on roughly $1.7 billion in revenue over the past 12 months.
Existing CBS shareholders will be allowed to exchange shares for CBS Radio shares.