Terms of the deal weren't immediately available.
Iloka, 28, was released in a cost-cutting move by the Cincinnati Bengals last week.
The Vikings are familiar with Iloka, who played for Vikings head coach Mike Zimmer for two seasons with the Bengals when Zimmer was defensive coordinator.
Andrew Sendejo is the starter at strong safety alongside Pro Bowler Harrison Smith. Iloka could unseat Sendejo with the first team and improve one of the NFL's best defenses. Both could play in a "big nickel" package, as Zimmer already said he's concerned with the team's depth at linebacker.
During free agency in 2016, Iloka visited with Zimmer and considered the Vikings, but Minnesota backed away when the Bengals made a $30 million offer.
Iloka was owed $5.3 million in salary and roster bonuses for 2018. His salary cap hit of $6.2 million was reduced by $4.4 million.
Originally a fifth-round pick from Boise State in 2012, Iloka has been a starter in all 76 games he has been active over the past five seasons, missing four games in 2015 because of ankle and groin injuries. He is coming off a year in which he had a career-best 80 tackles for the Bengals along with one interception.
In 83 career games, Iloka has totaled 343 tackles and nine interceptions.
--Field Level Media