OVERLAND PARK, Kan. (AP) — A mail-service drug prescription company in Overland Park has announced an expansion that will include adding 620 jobs to its current round of hiring, making the firm Johnson County’s fifth largest private employer.

OptumRx is expected to have about 2,100 employees at its mail and customer service center in 18 months, according to The Kansas City Star.

OptumRx has handled 48 million prescriptions since it opened its Overland Park facility in 2006. The 313,000-square-foot site was expected to process 13 million prescriptions this year.

“We are adding employees in virtually every position, from entry-level to highly experienced, from shipper to pharmacist,” said Larry C. Renfro, CEO of Optum, the parent company of OptumRx.  Company officials announced the expansion Wednesday.

OptumRx, which is part of UnitedHealth Group, has 13 million customers and expects to fill $23 billion worth of prescriptions this year. Besides Overland Park, the firm’s other large mail service center is in Carlsbad, Calif.