Thompson Coburn, St. Louis’ largest law firm, signed a 12-year lease to remain at U.S. Bank Plaza downtown after a two-year-long search effort.

Thompson Coburn Chairman Tom Minogue made the announcement at a news conference Tuesday afternoon at City Hall.

“When I walk the halls at Thompson Coburn, all the partners and staff want to be downtown,” Minogue said. The firm, which has 600 attorneys, was in talks earlier this year with the developers of Brown Shoe Co.’s new headquarters complex about relocating at Brown’s planned new campus at 8300 Maryland Ave.

Thompson Coburn leases 230,000 square feet of space at the U.S. Bank Plaza at 505 N. Seventh St., where it has been based since the office tower was built in 1975. The new lease is for 240,000 square feet of space and includes a planned $10 million renovation.

With the new lease, Thompson Coburn will have new upper floor exterior signage on the 36-floor building.

St. Louis Mayor Francis Slay said retaining Thompson Coburn is a big win for downtown’s ongoing revitalization efforts. “Having a prestigious law firm in downtown is good for the city’s image,” Slay said.

City and state officials put together a package of incentives to retain Thompson Coburn, including property tax abatement on new personal property, and sales tax exemption on construction materials for renovations to its office space. Deputy Mayor Barb Geisman estimated those two components of the incentive package will total $700,000.

Additionally, the state of Missouri, through the Missouri Development Finance Board, will help fund a new $15 million parking garage on the site of the existing plaza adjacent to the U.S. Bank Plaza building. The parking garage, which will be open to the public, will have a minimum of 360 new spaces, with some of the floors underground.