Final answer:
The three primary user groups of external state and local governmental financial reports as stated by GASB Concepts Statement No. 1 are the citizenry, legislative and oversight bodies, and investors and creditors.
Step-by-step explanation:
According to GASB Concepts Statement No. 1, the three groups of primary users of external state and local governmental financial reports are the citizenry, legislative and oversight bodies, and investors and creditors. The citizenry includes individuals and citizen's groups interested in government services, taxation, and the allocation of public resources. Legislative and oversight bodies require financial reports to inform policy and budgetary decisions, while investors and creditors need this information to make informed lending and investing decisions.