Minnesota State Highway 66 is a highway in south-central Minnesota, which runs from its intersection with Blue Earth County Roads 1 and 10 near Good Thunder and continues north to its northern terminus at its interchange with U.S. Highway 169 / State Highway 60 in the city of Mankato.

Highway 66 is 12 miles (19 km) in length.

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

Highway 66 follows Carney Avenue in the city of Mankato.

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

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

The route parallels the Maple River near Good Thunder.

The highway is legally defined as Legislative Route 256 in the Minnesota Statutes. It is not marked with this number.

Highway 66 was created in 1963. It was originally numbered State Highway 256 from 1949 to 1963.

The route was paved (as 256) by 1953.

The entire route is in Blue Earth County.