MainSource Bank plans to open its first Indianapolis branch in part of the former downtown home of Borders at the southeast corner of Meridian and Washington streets.

The Greensburg-based bank has signed a lease to take 9,500 square feet on the first and second floor of the northwest corner of the 17-story Barnes & Thornburg Building, bank CEO Archie Brown said in an interview.

The space has been vacant since early 2011, when the book retailer Borders Group Inc. closed the store as it went through bankruptcy. The law firm Barnes & Thornburg, which owns and has its headquarters in the building, has not yet signed a tenant for the remainder of the 22,000-square-foot Borders space, though industry sources expect the eventual tenant to be a restaurant.

The new tenant returns the building to its roots: It was completed in 1912 as a new headquarters for Merchants National Bank. Borders occupied the space for 10 years. The space previously housed a Paul Harris clothing store.

MainSource plans to operate a full-service retail bank branch beginning this fall in a 4,000-square-foot space on the first floor and a commercial banking and financial advising operation in 5,500 square feet on the second floor. The bank plans to recruit a staff of about 20.

"It's part of an overall plan of continued expansion," Brown said. "We felt like if we're going to get into the downtown Indianapolis market, this is the location for it."

The location gives the bank a billboard of sorts just south of Monument Circle along with the branch space itself. MainSource agreed to a 10-year lease with 5-year optional extensions, though officials would not reveal what they are paying. Borders was paying $25 per square foot, one of the highest rent rates downtown.

MainSource still must win approval for its plans to remodel the space, which include keeping an open staircase in place while giving it a new look, and adding new exterior signage. The building is listed on the National Registry of Historic Places.

MainSource operates 83 branches in Indiana, Illinois, Ohio and Kentucky, including five branches in Johnson County.

Brown said he expects the bank eventually will add more new branches in Marion County, but is unlikely to open newly built branches in the "over-banked" Hamilton County.

"We're going to be opportunistic," he said. "If this goes well, you can expect more."