Assessor County Updates

Last updated: July 30, 2026

Overview

Most counties certify property assessments on an annual or bi-annual cadence. However, in certain Northeast states (Connecticut, New Hampshire, Massachusetts, Maine, Rhode Island, and Vermont), assessments may be updated multiple times throughout the year at the township or jurisdiction level. When updates occur, ATTOM processes and publishes the refreshed county dataset and delivers updates as frequently as daily when new data is received. The Tax Assessor dataset also includes the latest available ownership information at the time of processing.

Details

Property assessment data is governed by county and local jurisdiction certification schedules.

Standard County Cadence

  • Most U.S. counties certify property assessments annually or bi-annually.

  • Certification establishes the official assessed values for the tax cycle.

  • Updates typically follow formal assessor sign-off and public posting.

Northeast Jurisdiction-Level Updates

In the following states, assessment updates often occur at the township or local jurisdiction level rather than strictly countywide:

  • Connecticut

  • New Hampshire

  • Massachusetts

  • Maine

  • Rhode Island

  • Vermont

Because townships within a county may certify on different schedules:

  • Multiple updated files may be received throughout the year.

  • When a township updates, the county file may be reissued.

  • ATTOM processes and publishes the refreshed dataset upon receipt.

Delivery Cadence

  • Update frequency depends on when source data is released.

  • Ownership information reflects the most recent data available at the time of processing.

Important Notes

Coverage

  • Annual certification is the standard for most U.S. counties.

  • Bi-annual certification is common in select regions.

Update frequency may vary based on:

  • Local assessor governance structure

  • Township versus county authority

  • State compliance requirements

  • Timing of certified assessment roll releases

Limitations

  • Multiple updates during the year do not indicate data instability or errors.

  • A lack of mid-year updates does not indicate missing data, as many counties update only upon certification.

  • Differences in update timing between counties do not indicate inconsistencies in ATTOM's processing.

Integration Guidance

  • Expect update frequency to vary by geography.

  • Design downstream systems to support incremental data refreshes.

  • Do not assume assessment values remain static throughout the calendar year.

  • If tracking ownership changes, use the most recently delivered dataset as the system of record.

  • Consider timestamp-based ingestion logic when processing data from high-frequency update counties.