Marine on St. Croix, Minnesota (Wikipedia)Marine on St. Croix or Marine on Saint Croix (/məˈriːn ɒn ˈseɪnt ˈkrɔɪ/ mə-REEN on SAYNT KROY) 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.