The Chicago Democrat wants the seat currently held by Forrest Claypool, who is leaving the post for a job with a health care company.
"I’m leaving Springfield to take on a battle where I think more warriors are needed," Fritchey said Tuesday.
The 45-year-old has served in the Illinois General Assemby for 13 years and is supported by Claypool and Mike Quigley, the former commissioner who defeated Fritchey earlier this year in the election for Rahm Emanuel's congressional seat.
Emanuel, you'll recall, is now President Barack Obama's White House Chief of Staff.
Fritchey said he'd like to focus on property tax reform and environmental issues on the board, the Chicago Sun-Times reported.
Quigley joined Fritchey at during the announcement and used the County Board's failure to override Todd Stroger's veto of a sales tax repeal as a selling point.
"This drama wouldn't be necesssary if a measure that Rep. John Fritchey introduced -- he and I worked together on this -- to reduce the number of votes necessary to override a president's veto in Cook County," Quigley said.
Quigley said their legislation would have ensured that "no (County Board) president thinks that they are above due process, no president thinks they're above a legislative process, (and) that they can't ride in an autocratic form over the wishes of the public, a majority of the public."
"Had that measure passed, so many other reform measures would have gone forward," he said.
Claypool said Fritchey was "ideally-suited to not just carry on, but build upon, the work Mike and I have done on the County Board."
Fritchey was an early critic of indicted former Gov. Rod Blagojevich, and took a jab when asked about the former governor's new tell-all book.
"I stopped reading the comics, you know, a long time ago," he said.
The Primary Election will be held next February.