The present municipality was created during the local government reform in the late sixties and early seventies. Already in 1967 the City of Öregrund joined the City of Östhammar in a common municipality. It was the first time a former city joined another local government unit. By 1971 the new combined city became a municipality of unitary type and in 1974 more units were added.
All towns with over 200 inhabitants in 2000, from Statistics Sweden.