Johnson immediately was taken into custody. He could have been sentenced to up to a year behind bars. Johnson, who pleaded guilty to violating his probation, also must pay a $2,500 fine.
Johnson was arrested on misdemeanor weapons charges Dec. 14 after police raided his home in the Lake County town of Gurnee, about 40 miles northwest of Chicago, and found six unregistered firearms.
At the time, he was on probation in a November 2005 Cook County case. In that case, he'd pleaded guilty to a misdemeanor charge stemming from an arrest in which a nightclub valet reported seeing Johnson with a handgun in his sport utility vehicle.
Dressed in a gray suit, Johnson arrived at the courtroom Thursday with coach Lovie Smith and All-Pro linebacker Brian Urlacher, who testified on Johnson's behalf.
"Tank knows he's in a situation where he can't get into any other trouble," Smith said, adding jail time would be "devastating" for the player's career. "And he's let me know there won't be any more."
Before he was sentenced Johnson pleaded with Cook County Circuit Judge John Moran for leniency.
"Your honor, I don't believe I'm a man who belongs in jail," he said.
But prosecutor Rick Cenar said jail time was appropriate.
"Just because he's a professional football player and plays for the Chicago Bears doesn't put him above the law," Cenar said.
Johnson's bodyguard, Willie B. Posey, was arrested on felony drug charges after the raid on Johnson's home. Posey was shot and killed two days later during an early morning fight while he and Johnson were at a nightclub in Chicago.
The Bears suspended Johnson for one game for being out at the club.
He has been under house arrest since the raid but was permitted to attend practice and travel to Miami for the Super Bowl, where the Indianapolis Colts beat the Chicago Bears 29-17.
Just days after returning from Miami, Johnson pleaded guilty to violating his probation in the 2005 case. He has pleaded not guilty to the Lake County charges in the latest arrest.
More to come on this breaking story as is becomes available to BearReport.com.