The Constitution of the United States of America does not mention local governments. Local governments are created by and regulated by the states. This means that to speak about cities or other forms of local government in the United States is to speak about fifty different legal and political situations.
The states outline the powers of municipal governments. This description of annexation is a broad summary of practices across the United States. The state municipal leagues can provide specific information about annexation procedures for particular state constitutions.
Annexation is a procedure for bringing unincorporated areas into a city or additional service areas into a special purpose district. An annexation area is usually adjacent to an incorporated city or a special purpose district. Annexation preserves a growing urban area as a unified whole. It enables urbanized and urbanizing areas to unite with the core city to which the fringe is socially and economically related. Industrial, commercial, and high-income residential areas may offer a high level of urban services, while the low and moderate-income residential satellite city may strain to provide minimal services. In both instances, satellite city residents draw on the resources of the core city without contributing toward the cost of these resources. Annexations facilitate the full utilization of existing municipal resources. City administrative and technical personnel are able to address the fringe area's municipal needs, and do this in a manner consistent with policies of the annexing city. In some cases, annexation may precede urbanization as a means of capturing anticipated growth.
Sources:
Municipal Research & Services Center of Washington, Annexation Handbook: Information for Cities and Towns in Washington State. Seattle, WA: Municipal Research and Services Center of Washington, 1995.
Municipal Technical Advisory Service, Annexation Guidelines: How to reduce negative impacts. Knoxville, TN: The University of Tennessee, Institute for Public Service, (1999)