Radium, Minnesota. Radium is a ghost town in section 19 of Comstock Township, Marshall County, Minnesota, United States. It was built alongside the Minneapolis, St. Paul and Sault Ste. Marie Railroad (Soo Line Railroad) branch line built in 1905 from Thief River Falls, Minnesota, to Kenmare, North Dakota. (This line still operates under the aegis of the Northern Plains Railroad.) The place was named for the element radium.