The 186-year-old campus on Hammond and Union Streets includes the home of former vice president Hannibal Hamlin.
The property was put on the market about two years ago, because the campus was so expensive to maintain.
The school has since moved to the campus at Husson College.
Bangor developer Paul Cook says he plans to rent apartments and find businesses to fill the space at the old site.
He and his partner will probably sell the Hamlin House.