ST. LOUIS -- The Silicon Valley firm Square Inc. has signed a 15-year lease for the downtown building that will soon be vacated by the St. Louis Post-Dispatch, with plans to more than double its St. Louis workforce.

Square Inc. was founded by Twitter co-founder Jack Dorsey along with Jim McKelvey. Both are St. Louis natives.

Square already employs about 500 people in St. Louis' Central West End -- the payment processing firm's second-largest office behind its San Francisco headquarters. The Post-Dispatch reported those workers will eventually move to the downtown building, which has room for up to 1,400 workers.

Dorsey called St. Louis "an amazing home and partner."

The Post-Dispatch is moving to a nearby building. Its longtime home at 900 N. Tucker Blvd. was sold to McKelvey's StarLake Holdings in September.

Information from: St. Louis Post-Dispatch, http://www.stltoday.com