Tillman's 22-yard return in the second quarter proved to be game-winning score for the Bears (8-8), who snapped a five-game losing streak to end the season.
The Vikings (3-13) were led by defensive end Jared Allen, who collected 3 1/2 sacks for a total of 22 on the season. That broke a club record set by Chris Doleman in 1989.
Allen finished only 1/2 sack short of the NFL record set by former New York Giant Michael Strahan in 2001.
The Vikings' Joe Webb picked up 200 passing yards on 15-of-29 efficiency with two interceptions after coming in to replace Christian Ponder.
Ponder was knocked out of the game on a second-quarter hit from defensive end Israel Idonije.