Saint Onge (pronounced "saynt AHNJ'"[4]) is an unincorporated community and census-designated place (CDP) in Lawrence County, South Dakota, United States.

[9] St. Onge is in northeastern Lawrence County, along South Dakota Highway 34, which leads northwest 12 miles (19 km) to Belle Fourche and southeast 7 miles (11 km) to Interstate 90 at Whitewood.

Spearfish, the largest community in the county, is 12 miles (19 km) to the southwest.

According to the U.S. Census Bureau, the St. Onge CDP has an area of 1.4 square miles (3.5 km2), all land.

False Bottom Creek flows northwest to the Redwater River, which in turn is a tributary of the Belle Fourche River, flowing east to the Missouri.