Route 370 was considered to be Interstate 370 but AASHTO would only allow it if it was renumbered Interstate 870. MODOT did not want this and kept it as Route 370.
On December 16, 1992, the first section of the highway opened allowing direct access to St. Charles at Route 94 from I-270. It replaced the crumbling Old St. Charles Bridge that carried Route 115 traffic. On April 1, 1993, the road was designated as Route 370. In 1993, the Great Flood of 1993 surrounded much of the highway which is built on top of an embankment. As the flood waters surrounded the highway, many of the new exits had been shut down because the roads it connected to were underwater. Despite the flood, construction resumed on the highway until it was completed in 1996.