"We wish Jared the best as he turns to the next chapter of his NFL career," Vikings general manager Rick Spielman said in a statement. "Not only was he an outstanding player on the field for the Vikings over his six seasons, but he also helped change lives in our community through his charitable work. Jared will always be a fan favorite, and we hope he stays involved with the Vikings franchise in years to come."
Now Vikings fans will see what it's like to watch Allen play for another team in the NFC North.
"We are extremely happy for Jared, his wife, Amy, our fans and the Chicago Bears that Jared has agreed to terms and will be joining the Bears family," general manager Phil Emery said. "This is another important step in our continued efforts to build our team towards a championship level."
Allen also had visited the Dallas Cowboys and Seattle Seahawks during free agency and had toyed with the idea of retiring. He had said toward the end of the 2013 season that he'd stop playing before he'd accept a role as a situational pass-rusher.
But as he replaces the recently released Julius Peppers in Chicago, it seems Allen will have a chance to continue getting a heavy share of playing time -- after playing 93 percent of the Vikings' snaps from 2008 to 2013 -- and securing his spot on the all-time sacks list.
Allen needs 4.5 sacks to move into sole possession of 10th place, and he could climb to as high as fifth next season and pass Strahan if he's able to record 13.5 sacks.
He needs 72.5 sacks to tie Bruce Smith for the career record, but considering he hasn't been below 10 sacks in a season since 2006, he has a chance to significantly add to his numbers.
The Bears will introduce Allen on Monday.
ESPN.com Ravens reporter Jamison Hensley contributed to this report.