The Lamoille River is a river which runs through northern Vermont and drains into Lake Champlain. It is about 85 miles in length, and has a drainage area of around 706 square miles. The river generally flows southwest, and then northwest, from the water divide of the Green Mountains. It is the namesake of Lamoille County, Vermont, through …The Lamoille River is a river which runs through northern Vermont and drains into Lake Champlain. It is about 85 miles in length, and has a drainage area of around 706 square miles. The river generally flows southwest, and then northwest, from the water divide of the Green Mountains. It is the namesake of Lamoille County, Vermont, through which it flows. The river was the basis of the name of the now-defunct Lamoille Valley Railroad Company, successor to the St. Johnsbury and Lamoille County Railroad.