The highway is currently known as Blue Earth County Road 1 (CSAH 1).

Highway 66 served as a north–south route between Mankato and Good Thunder in south-central Minnesota, although it did not actually enter the latter city.

The route passed near the town of Skyline, adjacent to Mankato.

Highway 66 crossed the Le Sueur River, south of Mankato.

The highway was legally defined as Legislative Route 256 in the Minnesota Statutes.