The Riverside Shipyard was the ground-based Starfleet shipyard 2-1A located in Riverside, Iowa, Earth. The Riverside construction zone was under the SFC Division, United Federation of Planets, Sector 47. It was considered a maximum security zone; intruders could be met with lethal force. (Star Trek)
In the mid-2250s, the USS Enterprise was constructed at the Riverside Shipyard. The shipyard was also an embarcation point from where Starfleet Academy cadets would travel to their training facilities. According to the ship's dedication plaque, although constructed in Iowa, the Enterprise was launched from the San Francisco Fleet Yards.
In 2255, James T. Kirk boarded the military shuttle Bardeen at the Riverside Shipyard after Christopher Pike dared him to enlist in Starfleet and do better than his father the night before at the nearby Shipyard Bar. (Star Trek)
The first teaser trailer for Star Trek premiered with the release of Cloverfield (2008), depicting scenes of the Enterprise being constructed at the Riverside Shipyard.
According to co-writer Roberto Orci: "Shortly after the heroic death of George Kirk, the Iowa shipyards were erected by Starfleet to honor and commemorate the sacrifice. Hence, the Kelvin salt shaker in the diner, etc...." 
According to the novel Star Trek, the decision was more a matter of location, as central Iowa was close to the Mississippi River and a still-industrial Midwest, but sufficiently isolated that a catastrophic accident would endanger few people outside of the shipyard itself.
According to the original art for Balthazar Edison's personal file in Star Trek Beyond, a construction contract for the USS Franklin was written at the Riverside Shipyard in 2255, which is the year the Enterprise was under construction there, and long after the Franklin was built.