County subdivisions are the primary divisions of counties and their equivalent entities for the reporting of decennial census data. They include census county divisions, census subareas, minor civil divisions, and unorganized territories. The 2013 TIGER/Line Shapefiles contain a 5-character numeric FIPS code field for county subdivisions and an 8-character numeric ANSI code.

Legal Entities
Minor Civil Divisions (MCDs) are the primary governmental or administrative divisions of a county in many states. MCDs represent many different kinds of legal entities with a wide variety of governmental and/or administrative functions. MCDs include areas variously designated as American Indian reservations, assessment districts, barrios, barrios-pueblo, boroughs, census subdistricts, charter townships, commissioner districts, counties, election districts, election precincts, gores, grants, locations, magisterial districts, parish governing authority districts, plantations, precincts, purchases, supervisor's districts, towns, and townships. The Census Bureau recognizes MCDs in 29 states, Puerto Rico, and the Island areas. The District of Columbia has no primary divisions, and the incorporated place of Washington is treated as an equivalent to an MCD for statistical purposes (it is also considered a state equivalent and a county equivalent).

In 23 states and the District of Columbia, all or some incorporated places are not part of any MCD. These places also serve as primary legal subdivisions and have a unique FIPS MCD code that is the same as the FIPS place code. The ANSI codes also match for those entities. In other states, incorporated places are part of the MCDs in which they are located, or the pattern is mixed—some incorporated places are independent of MCDs and others are included within one or more MCDs.

The MCDs in 12 states (Connecticut, Maine, Massachusetts, Michigan, Minnesota, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, Vermont, and Wisconsin) also serve as generalpurpose local governments that generally can perform the same governmental functions as incorporated places. The Census Bureau presents data for these MCDs in all data products for which place data are provided.

In New York and Maine, American Indian reservations (AIRs) exist outside the jurisdiction of any town (MCD) and thus also serve as the equivalent of MCDs for purposes of data presentation.

Statistical Entities
Census County Divisions (CCDs) are areas delineated by the Census Bureau in cooperation with state officials and local officials for statistical purposes. CCDs are not governmental units and have no legal functions. CCD boundaries usually follow visible features and, in most cases, coincide with census tract boundaries. The name of each CCD is based on a place, county, or well-known local name that identifies its location. CCDs exist where:

There are no legally established minor civil divisions (MCDs)
The legally established MCDs do not have governmental or administrative purposes
The boundaries of the MCDs change frequently
The MCDs are not generally known to the public

CCDs have been established for the following 20 states:
Alabama
Arizona
California
Colorado
Delaware
Florida
Georgia
Hawaii
Idaho
Kentucky
Montana
Nevada
New Mexico
Oklahoma
Oregon
South Carolina
Texas
Utah
Washington
Wyoming

Census Subareas are statistical subdivisions of boroughs, city and boroughs, municipalities, and census areas, the latter of which are the statistical equivalent entities for counties in Alaska. The state of Alaska and the Census Bureau cooperatively delineate the census subareas to serve as the statistical equivalents of MCDs.

Unorganized Territories (UTs) have been defined by the Census Bureau in 9 minor civil division (MCD) states and American Samoa where portions of counties or equivalent entities are not included in any legally established MCD or incorporated place. The Census Bureau recognizes such separate pieces of territory as one or more separate county subdivisions for census purposes. It assigns each unorganized territory a descriptive name, followed by the designation “unorganized territory” and county subdivision FIPS and ANSI codes. Unorganized territories are recognized in the following states and equivalent areas:
Arkansas
Indiana
Iowa
Maine
Minnesota
New York
North Carolina
North Dakota
South Dakota

Undefined county Subdivisions—In water bodies, primarily Great Lakes waters and territorial sea, legal county subdivisions do not extend to cover the entire county. For these areas, the Census Bureau created a county subdivision with a FIPS code of 00000 and ANSI code of 00000000 named “county subdivision not defined.” The following states and equivalent areas have these county subdivisions:
Connecticut
Illinois
Indiana
Maine
Massachusetts
Michigan
Minnesota
New Hampshire
New Jersey
New York
Ohio
Pennsylvania
Rhode Island
Wisconsin
Puerto Rico

New England City and Town Area (NECTA) Codes — The 2013 county subdivision shapefiles also contain fields with codes for Combined New England city and town area, New England city and town area, and New England city and town area division. The NECTAs are delineated by whole county subdivision, thus county subdivision records can be merged to form these areas without having to acquire the individual NECTA shapefiles.