A special census is a basic enumeration of population, housing units, group quarters and transitory locations, conducted by the U.S. Census Bureau at the request of a governmental unit. They are conducted on a cost-reimbursable basis. The U.S. Census Bureau's authority to conduct special censuses is specified in Title 13, United States Code, Section 196.

For special census purposes, a governmental unit is defined as the government of any state, county, city, or other political subdivision within a state, or the government of the District of Columbia — or the government of any possession or area — including political subdivisions, American Indian Reservations, or Alaskan Native villages.

For the 2020 Special Census Program, the Census Bureau will use an internet self-response instrument for respondents to self-respond to the Special Census Questionnaire. Respondents will have a set number of weeks to respond to the Special Census Questionnaire using the internet self-response instrument. At the start of the special census, the Census Bureau will send an invitation letter to known housing units in the governmental unit’s special census area with information needed to respond online. Reminder letters and postcards will be sent to each known housing unit to encourage self-response and provide information needed to do so.

After the end of the special census self-response period, the Census Bureau will conduct followup operations in the field to enumerate housing units that did not respond using the internet self-response instrument as well as housing units that did not receive mailed materials. These housing units will be contacted by a field representative who will conduct a special census interview using a paper questionnaire.

The field operations will also enumerate group quarters and transitory locations in the governmental unit’s special census area using paper questionnaires.

During the field operations, special census field representatives will conduct listing to verify the current address lists for the special census area and add, delete, or update the addresses of living quarters as needed, based on their observation of housing units, transitory locations, and group quarters. The Special Census Questionnaires will collect the same information that was gathered during the 2020 Census.

If requested, during special census operations the Census Bureau will also enumerate people living in group situations. Group quarters are places where people live or stay in a group living arrangement. These places are owned or managed by an entity or organization that provides residents with housing and/or services. Some examples of group quarters include: college/university student housing (i.e., dorms, residence halls, etc.), residential treatment centers, skilled nursing facilities, group homes, military barracks, correctional facilities, and maritime and military vessels.

A transitory location is a place people are unlikely to live year-round. Transitory locations include campgrounds, RV parks, marinas, hotels, motels, racetracks, circuses, and carnivals. Each transitory location has multiple transitory units, which can be rooms in a lodging facility or spaces where a tent, boat, RV, or other structure may be parked or located. An occupied transitory unit is considered a housing unit if there is at least one person who usually resides there. If no one is staying at a transitory unit, that transitory unit is considered unoccupied and is not marked as a living quarters. Similarly, a transitory unit is not tabulated as a housing unit if all people staying there report a usual home elsewhere. Anyone who reports a usual home elsewhere should be counted at that home.

Local officials frequently request a special census when there has been a significant population change in their community due to annexation, boundary changes, growth, or the addition of new group quarters facilities after the 2020 Census.

Many states use Special Census population statistics to determine the distribution of state funds to local jurisdictions.

Local jurisdictions may also use the data to plan new schools, transportation systems, housing programs, or water treatment facilities.

A special census, however, cannot change the 2020 Census results.

The Special Census program is typically on hiatus during Decennial Census years. During the hiatus the U.S. Census Bureau updates program materials and systems. The Census Bureau has been authorized to conduct special censuses since 1903; the nation's first special census was conducted April 15, 1915.

Although the method in which special censuses are conducted has changed, the basic objective remains the same: to obtain updated population and housing counts.

The 2020 Special Census Program will accept requests for cost estimates from governmental units starting in March 2023 and continuing through May 2027. Data collection will start no earlier than January 2024 and will continue through September 2028.