Massachusetts in the 2026 midterms: the state’s files are on the way

Alphabetical. Each entry gives the county’s registrations against the Census count of adult citizens, its ballots, and its swing since 2024, with the file each figure comes from.

Every figure on this page is computed from the files listed below when the page is built. The registration count is the state’s own, under the state’s own label. The adult-citizen count is the Census Bureau’s citizen voting-age population from its special tabulation of the American Community Survey for 2020 to 2024, which carries a margin of error for every area; a county is “over within the margin” when its registrations pass the estimate by less than that margin.

The ratio to all adults uses the Census Bureau’s Vintage 2025 estimates of every resident of voting age, citizen or not, as of July 2025. Turnout is ballots cast divided by registrations, using the state’s own label for its ballots count; where a state publishes no ballots count, the votes in the race shown stand in, and the entry says so.

The swing is the Democratic share of the two-party vote in the 2026 race shown, minus the Democratic share in the 2024 presidential race, in percentage points. The race is the US Senate where the Democrat and the Republican each drew more votes than all other candidates together; otherwise the governor’s race; otherwise the US House, summed over each county’s contested districts. Votes are counted on the Democratic and Republican lines only; votes for the same candidates on other party lines are counted with the other candidates. Under ranked choice, first choices are used. The 2024 baseline is the MIT Election Data and Science Lab’s county file.

These pages describe the numbers. They are kept apart from the tests we registered in advance for our own analysis of the 2026 returns. Unofficial results move during the canvass; each figure carries the time of the file it came from, and the pages are rebuilt as states certify and post new registration files.