Ramsey County is adding a downtown St. Paul riverfront site, which once included the county jail overlooking the Mississippi River, to its bid to win the competition for Amazon’s second headquarters.

The Seattle-based firm is looking to start a parallel headquarters that could house as many as 50,000 workers over time. It’s seeking a site of at least 100 acres, and the Ramsey County site best suited for that is the immense tract in Arden Hills that once was home to the Twin Cities Army Ammunition Plant (TCAAP).

But Amazon also seems partial to urban sites with robust transit options. The 8-acre downtown site would be close to the light-rail Green Line and Union Depot, a hub expected to get busier as the metro area’s transitway network develops.

The bids, along with those of others from around the metro area, were due Friday to Greater MSP, the economic development outfit working with state officials to prepare a single Twin Cities bid that could include multiple prospects.

Louis Jambois, a consultant for Ramsey County and former director of the St. Paul Port Authority, was asked why the county should offer the 8-acre site when Amazon wants 100 acres.

“They do talk about 100 contiguous acres in one part of their request for proposals, but in another part they speak of using existing buildings or shovel-ready pads,” Jambois said. “We are taking that literally. If they want to cobble together multiple parcels as in Seattle, we have lots of space awaiting them here.”

Ramsey County is pitching the riverfront site as “iconic and highly visible,” with two parcels, the one that once included the jail and another that housed West Publishing before it moved to the suburbs.