Marine on St. Croix or Marine on Saint Croix is a city in Washington County, Minnesota, United States. The population was 689 at the 2010 census. It was founded in 1839 as Marine Mills. The city was the site of the first commercial sawmill on the St. Croix River. A substantial portion of the city is listed as a historic district on the National Register of Historic Places and by the state of Minnesota.

Washington County is a county in the U.S. state of Minnesota. As of the 2020 census, the population was 267,568, making it the fifth-most populous county in Minnesota. Its county seat is Stillwater. The largest city in the county is Woodbury, the eighth-largest city in Minnesota and the fourth-largest Twin Cities suburb.