RELATED: Chicago's Union Station area to get $1 billion makeover
Chicago Mayor Lori Lightfoot was among those who attended the 8:45 a.m. event in the Loop.
"Downtown Chicago is experiencing a building boom," Lightfoot said.
The 50-story office building will rise at 320 S. Canal St., on the block just south of the historic main train station terminal building, and create space for 22,000 office workers, she said. It will also become BMO Harris Bank's new U.S. headquarters.
It's just part of a larger Union Station development project.
The office tower is expected to be done by January 2022.