Highway 20 passes through the city of Cannon Falls and Douglas Township.

Its northern terminus is 400 feet west of Highway 50's junction with U.S. 61.

Highway 20 was designated and signed in 1920 from the Iowa border near Canton to its current northern terminus.

[3][4] U.S. Route 55 was established in 1927 along this road from the Iowa border to Cannon Falls.

When U.S. Route 52 was extended into Minnesota in 1934 to replace U.S. 55, the Highway 20 designation was removed from this portion of the highway, leaving only the section that remains today.