Annexation is the methodical extension of a city’s boundaries into adjacent unincorporated areas, and the corresponding extension of that city’s services to the areas encompassed by the new boundaries. In Utah, annexation is governed by state statutes that allow cities and towns to annex adjacent areas, once those areas contain certain urban development characteristics (population density, subdivision of land into smaller lots, development intensity).
See Municipal Certifications & County Boundaries on the Lieutenant Governor’s website for official documents.