“I do absolutely believe that the core of the region is downtown St. Louis,” Krewson said.

The Post-Dispatch building lease would give Square space for as many as 1,400 local employees, and the company plans to move all of its employees from Cortex to the downtown building within the next few years. Downtown, with a vacancy rate around 15 percent, has among the lowest office rental rates in the region, while Cortex is often much more expensive. Still, the St. Louis region is far cheaper than coastal markets where tech firms such as Square congregate.

Square is leasing nearly all of the 235,000-square-foot building, leaving only about 10,000 square feet open. StarLake has only just started to rehab the old newspaper building, so it could be more than a year before Square begins adding employees downtown.

Many of Square’s local employees are in compliance, customer support and other back-office functions. But the company has also begun hiring software engineers locally, significant because Dorsey and McKelvey in 2009 relocated the company to San Francisco because of difficulty finding the tech talent here to scale the business.