Johnson was limited to six appearances in 2019 because of a shoulder injury that brought his season to an early end, but he bounced back with a strong campaign in 2020.
The 25-year-old former Boston College standout recorded 105 total tackles, eight passes defended and one interception across 16 games. He earned a 85.6 overall grade from Pro Football Focus.
Johnson said he was "emotional" after the Rams' Divisional Round playoff loss to the Green Bay Packers because of the uncertainty about his future.
"Just not knowing what's going to happen, not knowing if the guys you've been with for four years, you're going to be with them again," he told reporters. "I guess we'll just go from there and see how it goes."
Johnson, a 2017 third-round pick, heads to free agency after tallying 350 tackles, 32 passes defended and eight interceptions in 54 regular-season appearances for L.A.
He'll be one of the top safeties available on the open market, and the Rams likely won't be able to match any of the long-term offers he receives because of their salary-cap situation. They're $29.6 million over a projected $185 million cap for 2021, according to Spotrac.
So the odds are Johnson will be suiting up for a new team next fall.