The Governmental Accounting Standards Board (GASB) is currently the source of generally accepted accounting principles (US GAAP) used by State and Local governments in the United States of America. As with most of the entities involved in creating GAAP in the United States, it is a private, non-governmental, organization.
The GASB has issued Statements defining GAAP for state and local governments since 1984. GAAP for the Federal government is defined by the Federal Accounting Standards Advisory Board.