What is a Census Block?

A Census block is the smallest unit of measure used by the U.S. Census Bureau to collect, tabulate and publish data for all households in the United States.

Blocks can be bounded by visible features like streets, streams and railroad tracks, as well as by non-visible boundaries like city, town, and county limits. Several blocks make up a block group, which are grouped into Census tracts.

What do Census blocks look like? Do they ever change?

Here is an image of Census blocks in New York. Blocks vary in patterns, sizes, shapesâ??they may be small in cities, or large in remote areas. They can correspond to city blocks, but their configuration is influenced by topography, water features, the land survey system, as well as the type and density of development.

Census blocks are unique to and can never cross the boundaries of a census tract. In 1990 the Census Bureau created the TIGER database to automate the delineation of blocks. This made them more consistent and accurate, and eliminated narrow slivers of land.

How are blocks used?

Census blocks allow you to track demographic changes on a very fine scale. 1990 was the first year that the entire country was divided into Census blocks. Prior to that, blocks were only used in select areas, but the idea of gathering data block by block began as early as 1920. Today, each block is given an identifying 4-digit number that identifies the location of the block by its block group. Today there are about 8,200,000 Census blocks in the U.S.