Square Inc.’s new Cortex district office in the @4240 building is officially in business.

The mobile payment company’s employees have been moving in since January, but the company, which was founded by St. Louis natives Jack Dorsey and Jim McKelvey, will hold a grand opening tonight (4240 Duncan Ave.) to mark the occasion.

Already, 150 people work in the Square’s 17,000 square feet of space in the Cortex facility, which was recently converted from a parking garage into office space for $850,000.

That makes it the second-largest Square office, trailing only the company’s headquarters in Silicon Valley.

Square’s future is going to be huge,” McKelvey said. “And we hope we will have continued growth in St. Louis and throughout the ecosystem.”

Square announced in September it would be opening a new St. Louis office, though the company had been quietly operating out of the [email protected] building under the fictitious name Balbis (another shape that looks like the letter H) for several months leading up to that announcement.

The company is well on its way to meeting its 200 employee headcount goal. “If you look at the trend line, we’ll hit our multiyear goal very, very early,” McKelvey said.

Terms of Square’s deal weren’t disclosed. Rent at the @4240 building typically runs about $19 per square foot.

Square currently has 13 open positions in business development, information technology and customer support.

Source: St. Louis Business Journal by Brian Feldt