Census block

A census block is the smallest geographic unit used by the United States Census Bureau for tabulation of 100-percent data (data collected from all houses, rather than a sample of houses). Several blocks make up block groups, which again make up census tracts. There are on average about 39 blocks per block group, but there are variations. Blocks typically have a four-digit number where the first number indicates which block group the block is in, for example Block 3019 would be in block group 3. The number of blocks in the United States including Puerto Rico is about 8,200,000.

Blocks are typically bounded by streets, roads or creeks. In cities a census block may correspond to a city block, but in rural areas where roads are fewer, blocks may be limited by other features. The population of a census block varies greatly, there are about 2,700,000 blocks with a population of 0, while a block with an apartment complex may have several hundred inhabitants.

Census blocks covering the entire country were introduced with the 1990 census. Prior to this, back to the 1940 census, only select areas were divided into blocks.

References

*U.S. Census Bureau. Information on geography and data for all blocks is provided at their [http://factfinder.census.gov/servlet/DatasetMainPageServlet?_program=DEC&_lang=en&_ts= Data Sets] website.
*Some statistics can be found in the Census Bureau's [http://www.census.gov/geo/landview/lv6help/pop_estimate.html description] of LandView 6 software.