Distribution of Museums by Discipline, FY 2014. Source: Museum Universe Data File, FY 2014 Q3, Institute of Museum and Library Services
According to the Institute of Museum and Library Services there are approximately 35,000 museums in the United States. The largest category of museum by “type” is Historical Societies, Historic Preservation, and Historic Houses and Sites.
Sources:
Government Doubles Official Estimate: There Are 35,000 Active Museums in the U.S.
Distribution of Museums by Discipline, FY 2014