Sinise was born in Blue Island, Illinois, son of Robert L. Sinise (born 1928), a film editor, and his wife Mylles (Alsip) Sinise (born 1928). His paternal grandfather was of Italian descent, Sinise's great-grandfather Vito Sinisi having immigrated from Ripacandida. Sinise briefly attended Glenbard West High School in Glen Ellyn, Illinois, and later graduated from Highland Park High School in Highland Park, Illinois, followed by Illinois State University. In 1974, Sinise and two friends, Terry Kinney and Jeff Perry, founded the Steppenwolf Theatre Company. Since then, Steppenwolf has showcased the talents of notable actors such as Joan Allen, Kevin Anderson, Gary Cole, Ethan Hawke, Glenne Headly, John Mahoney, John Malkovich, Laurie Metcalf, Martha Plimpton, Jim True-Frost, and most recently William Petersen. Sinise honed his acting and directing skills at Steppenwolf, and received a Joseph Jefferson Award for his direction of Lyle Kessler's play Orphans. That took him from Chicago to New York City, and then to London's West End, where he worked on more than thirty of the company's productions.