GlossaryGeography and community profiles
Annexation
Annexation is a legal action adding territory to a municipality or another eligible jurisdiction under applicable law.
Annexation is a legal action adding territory to a municipality or another eligible jurisdiction under applicable law. It changes a boundary rather than simply changing a place name or map label. The effect on services, taxes, representation, and records depends on the specific action, governing law, and effective date.
What changes in a dataset
The Census Boundary and Annexation Survey collects legal boundary changes used in Census geography. The Census geography glossary explains how annexations can affect legal and related statistical areas. A current map may therefore cover territory that was outside the municipality in an older report.
Annexation does not mean an increase in population was caused by people moving. Residents can become part of a municipality's total because the boundary changed around an existing community. Similarly, a city agency's reported activity can increase because its covered area expanded, even if conditions within the original territory stayed similar.
The timing of service transitions is a separate question. The legal boundary change and a provider agreement may have related but distinct implementation details. A reference page should not assume that every service transfers automatically in the same way.
Example
Hypothetical example: A city annexes an area with 2,000 existing residents. The next population presentation shows a larger municipal total, and police responsibility changes under the documented transition arrangement.
The additional residents are not necessarily new arrivals to the region. A comparison should identify the annexation before calling the municipal increase migration or interpreting a larger incident total as a change in risk. The police arrangement needs its own effective-date documentation.
Common confusion
Incorporation creates a municipality under the relevant process; annexation adds territory to an existing eligible entity. A merger or consolidation is another organizational change and should not be assumed from a boundary expansion.
A postal ZIP Code change does not itself annex territory. A statistical boundary update can reflect an annexation without being the legal action that created it.
Reading the record
Use the adopted legal document, affected-area description, effective date, and applicable service agreements. This definition does not provide a universal petition threshold, election rule, or approval deadline; state procedures differ. For trends and rates, align the incident geography and population denominator, and explain whether a series follows each year's boundaries or a reconstructed constant area.