An incorporated area may annex an unincorporated area or a portion of it. Property owners in an unincorporated area may request to be annexed to an incorporated area. In the latter case, at least two property owners of the unincorporated area, each owning at least one acre within a contiguous section of the unincorporated area, may petition the county to approve annexing a defined geographical area to an incorporated area. Generally, property owners who seek to annex are seeking more adequate government services or zoning benefits not available under the current governing unit. In some urban areas, townships have virtually disappeared as a result of annexation.
Annexation reduces a township government's tax base and inhibits revenue growth.
For example, if River Downs in Anderson Township were annexed by the City of Cincinnati, the Township would lose the property taxes paid by River Downs. Annexation does not require voter approval. It does, however, require petition by the majority of property owners involved in the annexation. Of the original area which became Anderson Township, the City of Cincinnati annexed Mt. Washington in 1911 and California in 1909. More recently annexation was used by the Village of Newtown to take 15 acres from Anderson Township and bring them into Newtown.