State Route 210 is part of Maine

Maine

Maine is a state in the New England region of the northeastern United States, bordered by the Atlantic Ocean to the east and south, New Hampshire to the west, and the Canadian provinces of Quebec to the northwest and New Brunswick to the northeast. Maine is both the northernmost and easternmost...

's system of numbered state highways. It runs in a 6.2 miles (10 km) loop from the intersection of U.S. Route 1

U.S. Route 1 in Maine

In the U.S. state of Maine, U.S. Route 1 is a major north–south state highway serving the eastern part of the state. It parallels the Atlantic Ocean from New Hampshire north through Portland, Brunswick, and Belfast to Calais, and then the St. Croix River and the rest of the Canadian border...

/State Route 164

Maine State Route 164

State Route 164 is part of Maine's system of numbered state highways. It runs from Presque Isle to Caribou. It begins at an intersection with U.S. 1 just north of Presque Isle, and ends at a junction of State Route 161 and U.S. Route 1 in Caribou...

 northeast and back around to U.S. 1 within Presque Isle

Presque Isle, Maine

Presque Isle is the commercial center and largest city in the sparsely populated Aroostook County, Maine, United States. The population was 9,692 at the 2010 census...

. The route was originally designated in 1925, and ran between Fryeburg and North Waterford

North Waterford, Maine

North Waterford is a village in the town of Waterford in Oxford County, Maine.-References:...

. During the renumbering, it became part of State Route 5

Maine State Route 5

State Route 5 is part of Maine's system of numbered state highways, running from the an intersection with Route 9 in Old Orchard Beach, to an intersection with Route 120 in Andover. Route 5 is long....

. In 1937/38, the number was applied to the loop built as a service road for the Northern Maine Sanitarium. Even after the closure of the sanatarium in the 1970s, the route remains open and in use.