Sources and method

1182 dates from 610 official pages. Most come from state law or a state revenue department, the rest from county treasurers, tax collectors and assessors.

How a date gets on the site

Every date is saved with the page it came from and a short quote from that page. A script reloads each page and looks for the quote. If the words are gone, the date comes off the site at the next build, even if it's probably still right. The checked date under each table is the last time that worked.

County names and codes are from the Census Bureau's 2020 county list. The towns under each county come from its place-by-county file.

What's missing

17 of 3,143 counties have no dated deadline yet. Some are in states where each county sets its due dates and few publish them on a page a script can read (Illinois and Virginia). Others have only the state's rules, such as the penalty, while the dates come from the county. Plenty of county sites also block automated requests, so a date a person can read there stays off until a page the script can load says the same thing.

In New England, and in much of New York, New Jersey and Pennsylvania, the town or school district sends the bill. A county page there can only show the state's rules. Special assessments and supplemental bills aren't covered.

Something wrong?

Offices change dates. If your bill says something different, go by the bill.