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- Jack Cafferty, political commentator for CNN
- L. Scott Caldwell, actress, Lost, Queens Supreme
- Bill Callahan, offensive coordinator and offensive line coach for the Dallas Cowboys
- Frances Callier, actress, comedian, I'm a Celebrity…Get Me out of Here!
- Joe Cannon, politician (Republican) and Speaker of the US House of Representatives
- Al Capone, gangster and bootlegger
- Antonio "Tony Bananas" Caponigro, consigliere of Angelo Bruno in the Philadelphia crime family
- Brian Cardinal, forward for the Dallas Mavericks
- Steve Carell, actor and comedian
- Amy Carlson, actress, Third Watch, Blue Bloods, Law & Order: Trial by Jury
- Terrence C. Carson, actor, voice actor, Living Single, Star Wars: Clone Wars, Life with Louie
- Maurice Carthon, former NFL running back primarily with the New York Giants
- James Cartwright, USMC general, Vice Chairman of the Joint Chiefs of Staff
- Dan Castellaneta, actor, The Simpsons, The Pursuit of Happyness, Happy Feet
- Anton Cermak, politician (Democrat) and Mayor of Chicago
- George Chandler (1898–1985), actor
- Jay Chandrasekhar, actor, comedian, film director
- Brenda Chapman, animator and film director, The Prince of Egypt
- Maurice Cheeks, former NBA point guard and current assistant coach for the Oklahoma City Thunder
- Judy Chicago, feminist artist and author
- Anna Chlumsky, actress
- Amy Chua, professor at Yale Law School and author of World on Fire and Day of Empire
- Danny Clark, linebacker for the New Orleans Saints
- Hillary Rodham Clinton, attorney and politician (Democrat), former First Lady, New York Senator and current U.S. Secretary of State
- Gary Cole (born 1956), actor, The Brady Bunch Movie, Office Space, Talladega Nights
- James M. Cole, U.S. Deputy Attorney General under President Barack Obama
- Gary Coleman, actor, Arnold Jackson on Diff'rent Strokes
- Doug Collins, head coach for the Philadelphia 76ers
- Sherron Collins, former NBA point guard
- Common, rap musician, songwriter, producer, actor
- George Connor, Hall of Fame offensive tackle/linebacker for the Chicago Bears
- Robert Conrad, actor, Hawaiian Eye, The Wild Wild West, Baa Baa Black Sheep
- Brian Cook, power forward for the Los Angeles Clippers
- Martin Cooper, the inventor of the modern cell phone
- Billy Corgan (born 1967), rock musician from Alternative Rock band The Smashing Pumpkins
- Don Cornelius, television show host, producer, creator of Soul Train
- John Coughlin, Politician (Democrat) and Chicago Alderman
- Cindy Crawford (born 1966), supermodel
- Casey Crosby, starting pitcher for the Detroit Tigers
- Jim Crowley, NFL player, head coach and College Football Hall of Famer
- Adrianne Curry, model and America's Next Top Model, Cycle 1 winner
- Eddy Curry, center for the Miami Heat
- Ann Cusack, actress, The Jeff Foxworthy Show, Maggie
- Joan Cusack, (born 1962), actress
- John Cusack, (born 1966), actor
Read more about this topic: List Of People From Illinois