style="font-weight : bold;">Cook County Social Club is an improv and sketch comedy ensemble formed in 2005 in Chicago, Illinois at I.O. Chicago Theatre (formerly Improv Olympic). Its members are Bill Cochran, Greg Hess, Brendan Jennings, and Mark Raterman. Cook County Social Club perform longform improvisation, taking a single suggestion from the audience, to create a fully improvised piece. Members of the ensemble also perform with The Second City's national touring company.

Well reviewed among Chicago theater critics, Cook County Social Club has been featured in Time Out Chicago, Chicago Reader, New City, Chicago Magazine and the The Bastion In 2005, Chicago Reader critic Ryan Hubbard wrote:

"The four performers of Cook County Social Club, directed by Jeff Griggs, are as brazenly committed to improv's 'affirm everything' mantra as any I've seen. Their dark, flamboyant comic sensibilities clearly aligned, they orchestrate black-comedy vignettes tethered to richly odd characters. But what most impressed me was how fluidly and creatively they transitioned between scenes, usually dangerous improv moments."

In 2007, Cook County Social Club partnered with Storyboard Productions to create original sketch material based on their improvisation.