Trapp has collected 20 senior national team caps for the United States as well.
"We are obviously delighted to get a player of his age, quality, experience and a current U.S. international," Loons coach Adrian Heath said in a club statement. "Wil made it very clear from the outset that this was the only club he wanted to go to. Having spoken with him at length, I know he's incredibly excited about our plans moving forward and which he's excited to be a part of.
"Speaking to his former coaches and managers, the most frequently used words were quality, professional, leadership and honesty. These qualities completely dovetail into the type of person we are looking to bring into our club as we try to improve on what was a successful last season."
Trapp, who was an MLS All-Star in 2016, joins a Minnesota United squad that advanced to the Western Conference final last season.
"I am delighted to be joining a team and club with high ambitions," Trapp said. "There is a great energy about this team and the Twin Cities' support. I am very excited to get to work and help this club achieve its goals."
Trapp has two goals and 19 assists in 206 career MLS matches (195 starts) with the Crew and Inter Miami CF.