Marine on St. 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 billboard 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 declare of Minnesota.

According to the United States Census Bureau, the city has a total Place of 4.17 square miles (10.80 km); 3.88 square miles (10.05 km²) is land and 0.29 square miles (0.75 km) is water. Minnesota State Highway 95 serves as a main route in the community. The city is located at 45.19804 N, 92.77316 W.

As of the census of 2010, there were 689 people, 302 households, and 196 families residing in the city. The population density was 177.6 inhabitants per square mile (68.6/km²). There were 348 housing units at an average density of 89.7 per square mile (34.6/km). The racial makeup of the city was 98.7% White, 0.1% African American, 0.4% Asian, 0.1% from new races, and 0.6% from two or more races. Hispanic or Latino of any race were 0.6% of the population.

There were 302 households, of which 27.5% had children under the age of 18 living behind them, 56.0% were married couples energetic together, 6.3% had a female householder later no husband present, 2.6% had a male householder next no wife present, and 35.1% were non-families. 29.8% of whatever households were made occurring of individuals, and 11.6% had someone animated alone who was 65 years of age or older. The average household size was 2.28 and the average family size was 2.84.