Contra Costa County Property Taxes: December 10 Deadline to Avoid 10% Penalty

MARTINEZ / CONTRA COSTA COUNTY — November 7, 2026. Property owners in Contra Costa County have until 5 p.m. Thursday, December 10, to make their first installment of 2026–27 secured property taxes without incurring a late penalty.

Two installment deadlines

The first installment became payable November 1 and becomes delinquent after December 10. An unpaid first installment triggers a 10% penalty. The second installment is payable February 1, 2027, and becomes delinquent after April 10, 2027, with a 10% penalty and $20 administrative charge, subject to legal weekend or holiday adjustments. Owners may pay both installments early if they prefer.

Ways to pay

County Treasurer-Tax Collector Dan M. Mierzwa lists online payment through the official tax portal, payment by phone at 925-608-9500, checks by mail, in-person service at 625 Court Street, Suite 100, Martinez, and a secure drive-through drop box on the Main Street side of that building.

Watch fees and postmarks

The office honors qualifying USPS postmarks for mailed payments, but a late-arriving letter without timely postmark evidence may lead to penalties. Credit and debit cards have convenience charges; other methods may have different terms. Failure to receive a bill does not eliminate the tax obligation. Customers should verify their parcel and amount through official county systems rather than unsolicited payment links.

Source: Contra Costa County official notice.

YOUR LOCAL NEWSPAPER NEEDS YOU

Help this community newspaper grow

Your support helps build coverage for the people and places this local newspaper serves.

Donate once by card ↗

Help Martinez News grow Help strengthen reporting on Martinez: community voices, important decisions and local life.

Support Martinez News

Choose how to support Martinez News:

Credit / Debit Card via Stripe

Choose an amount from $1. One-time support through the publisher's LINKERNO Stripe account.

Continue with PayPal Continue with Zelle

Zelle payments go to Vitaly Ataev Troshin. Please verify the recipient in your bank before sending. Availability depends on your bank.

Optional reader support. When possible, add “Martinez News” to the payment note. Contributions are not advertised as tax-deductible. Support does not influence editorial decisions.

Optional support through the publisher. Contributions are not advertised as tax-deductible and never buy editorial influence.

Martinez News — Your Community Newspaper

Have a correction, news tip, local announcement, or story to submit? Contact our editorial team. All submissions are reviewed before publication.