The lakefront, four-bedroom home comes with 500 feet spanning Vermont's Lake Champlain.
His other homes are in Burlington, Vermont, and Washington, D.C.
Some Twitter users said that based on his campaign platform and political values of democratic socialism, it was a hypocritical move.
Among the headlines:"Bernie Sanders' third home puts a new spin on 'socialism' in America."
Combating rumors that Sanders used campaign donations to fund his purchase, his wife told a local news outlet that they sold another property to get the money for the new house.
"My family had a lake home in Maine since 1900, but we hadn’t had the time to go there in recent years, especially since my parents passed away," Sanders’ wife, Jane O’Meara Sanders, said a written statement. "We finally let go of it, and that enabled us to buy a place in the islands -- something I've always hoped for."