Joey "The Clown" Lombardo, 76, was caught in suburban Elmwood Park and was expected to spend the night in a Chicago jail, said FBI spokesman Ross Rice.
Lombardo's lawyer said his client will appear at a detention hearing Tuesday.
"Osama bin Laden has a better chance of getting bond," said Rick Halprin, Lombardo's attorney. "So, it will be a formality."
Federal agents grabbed Lombardo after they caught him meeting with someone they had under surveillance, the Chicago Sun-Times reported Friday night on its Web site, citing FBI officials.
Lombardo and 13 others were indicted in April as a result of a long-standing investigation aimed at clearing unsolved mob hits.
The indictment charges that Chicago hoodlums and mob associates conspired in at least 18 unsolved murders, including that of that of Tony "The Ant" Spilotro, once known as the Chicago Outfit's man in Las Vegas, and his brother Michael.
Joe Pesci played a character based on Tony Spilotro in the 1995 Martin Scorsese movie "Casino."
Lombardo and Frank "the German" Schweihs, are specifically named in the 1974 murder of Daniel Seifert. Schweihs, a 75-year-old reputed mob enforcer, was captured in Kentucky last month after eight months as a fugitive.