Le Mars is a city in and the county seat of Plymouth County, Iowa, United States. It is located on the Floyd River and northeast of Sioux City. The population was 9,826 at the 2010 census.Le Mars is the home of Wells' Dairy, the world's largest producer of ice cream novelties in one location and is the self-proclaimed "Ice Cream Capital of the World". Wells is best known for its Blue Bunny products.