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 The Census Bureau requires that the MCDs encompass as much of the geographic area of a State as possible. Where the MCD coverage is incomplete, the Census Bureau attempts to supplement the MCD coverage with an entity or entities that are MCD equivalents. There are a few States where the Census Bureau must use more than one type of MCD; for example, in Illinois it uses 1,434 townships and 243 election precincts (see ). In the portions of MCD States where no MCDs exist, the Census Bureau establishes UTs (see the “” section in this chapter).

The Census Bureau prefers that the MCDs in a State remain relatively stable from one decennial census to another, with only minor changes in their boundaries and areas. If there are massive or widespread changes, the geographic pattern of subcounty governmental units or administrative subdivisions is disrupted and the historical comparability of the data is impaired. When that happens, the Census Bureau may encourage the appropriate State officials to consider replacing the MCDs with CCDs.

The Census Bureau recognizes two types of geographic entities that, for statistical purposes, are equivalent to MCDs—independent incorporated places and UTs. Although these two classes of entities are not, strictly speaking, MCDs, the Census Bureau treats them as MCDs in order to include all of a State’s population and land area within the county subdivision level for data presentation purposes. In addition, there are anomalous situations in which miscellaneous types of geographic entities are equivalent to MCDs (see the “” section in this chapter).

These are incorporated places with governments that function independently from the jurisdiction of the surrounding MCD or MCDs. They do not receive governmental services from any MCD, except when they undertake to contract for such services. Their inhabitants do not pay taxes to any MCD, nor do they vote County Subdivisions8-15