Census 2010-2020 Block Relationship Files

We use the files for the 50 states and the District of Columbia. Confirmed against the Bureau's own directory listing on 2 August 2026, this is the complete series for that universe rather than a partial download.

The Island Areas are not published in it. American Samoa, Guam, the Northern Mariana Islands and the U.S. Virgin Islands were enumerated under a separate program, so 132 census tracts from 2010 in those areas have no block-level counterpart here. Those tracts also have no American Community Survey data, so the gap has no practical effect on what Birdseye reports.

Tract boundaries changed between the 2010 and 2020 censuses: some tracts were split, some merged, and many shifted. Any measure compared across that boundary change has to be put on a single set of boundaries first, or the comparison is between two different pieces of ground.

We use this file, together with 2010 block population and housing counts, as the basis for placing older tract-level data onto current tract boundaries. It is a geographic reference only and produces no metric of its own.

Harmonizing across a boundary change is an approximation, not a restatement. Older figures expressed on current boundaries carry more uncertainty than figures published on those boundaries directly, and that uncertainty is largest where tracts changed the most.

Per Census Bureau citation policy, the Bureau is cited as the source of the original geographic data only, and is not responsible for figures we derive from it.