Cowlitz County property tax bills come due in two installments each year: the first half by April 30 and the second half by October 31. Your bill is your January 1 assessed value multiplied by the combined levy rate of every taxing district covering your parcel, and missing a deadline starts interest running immediately, at 9 percent a year on most homes and 12 percent on other property.1Washington State Legislature. RCW 84.56.020 – Taxes Collected by Treasurer
When Taxes Are Due and How to Pay
If your total annual tax is less than $50, the whole amount is due April 30. For anything $50 or more, you can split it between the two deadlines.2Cowlitz County, WA. Important Dates
To look up a balance or pay online, you need your property ID number, not the parcel number. The two are different, and the Treasurer’s system will only accept the property ID. Both appear on the annual tax statement mailed to your address and in the county’s online property search.
The Treasurer accepts payment several ways:3Cowlitz County, WA. Options for Paying Property Taxes
- By mail to Cowlitz County Treasurer, 207 4th Ave. N, Kelso, WA 98626. The envelope must be postmarked by the deadline.
- Online or by phone at 1-844-965-0200. E-checks cost $2.00. Credit and debit cards carry a 2.4 percent processing fee with a $2.00 minimum, charged by the third-party processor.
- By drop box at the north and south entrances of the Administration Building at 207 4th Ave. N, or the drive-up box in the north parking lot. Check, cashier’s check, or money order only. No cash.
If a mortgage servicer pays your taxes from escrow, confirm after each deadline that the payment actually posted. Check the Treasurer’s website rather than assuming. Servicer mistakes do happen, and the interest clock does not care who was supposed to pay.
When a deadline lands on a weekend or holiday, verify the adjusted date with the Treasurer’s office. One day late counts as late.
How Your Tax Bill Is Calculated
Every property in Cowlitz County is assessed at 100 percent of its true and fair market value as of January 1 each year.4Washington State Legislature. RCW 84.40.030 – Basis of Valuation The Assessor estimates that value using recent sales of comparable properties, the condition of your property, and local market trends.5Cowlitz County, WA. Assessor Adding a room, replacing a roof, or rising prices in your neighborhood all show up in the next assessment.
The tax itself is that assessed value multiplied by the combined per-thousand-dollar rate of every district covering your parcel: the county, your school district, fire district, library district, and any others. Each district sets a budget and the county calculates the rate needed to fund it. Washington’s constitution caps the combined regular, non-voted levy rate at $10 per $1,000 of assessed value, but voter-approved levies can push the effective rate higher. Cowlitz County publishes detailed levy rate reports each year broken down by tax code area, because the exact rate depends on which districts apply to your parcel.
A rising assessed value does not automatically mean a proportionally higher bill. When values rise across the board, levy rates tend to drop to keep total collections within each district’s certified budget. Your share of the burden shifts based on how your value changed relative to everyone else’s.
What Happens If You Pay Late
Interest runs from the day a payment becomes delinquent until the balance is paid. For residential property with four or fewer units per parcel, including manufactured homes, the rate is 9 percent annually, or 0.75 percent per month. For all other property, including commercial and residential with more than four units, the rate is 12 percent annually, or 1 percent per month.1Washington State Legislature. RCW 84.56.020 – Taxes Collected by Treasurer
Non-residential property, residential with more than four units, and personal property also face two penalty milestones in the tax year: 3 percent on June 1 and an additional 8 percent on December 1. Residential property with four or fewer units has been exempt from these penalties since 2023, though the interest still applies.
The charges stack. A business owner who misses April 30 on a $5,000 bill would owe the original tax, 12 percent annual interest, and 11 percent in combined penalties by year’s end.
Three Years Delinquent Means Foreclosure
If property taxes remain unpaid for three years, the Treasurer is required to issue a certificate of delinquency and begin foreclosure.6Washington State Legislature. RCW 84.64 – Lien and Sale of Property for Delinquent Taxes This is not theoretical. In June 2025 the Treasurer initiated foreclosure against 24 parcels with 2022 and prior taxes owing, and 11 of those went to auction in December 2025.7Cowlitz County, WA. Foreclosure
After the certificate issues, the county notifies the owner and any lien holders and gives them a chance to pay the full delinquent balance plus interest, penalties, and costs. If no one pays, the property is sold at public auction to recover the debt. If you are behind and cannot pay in full, call the Treasurer’s office early. Once foreclosure begins, the costs grow and the options narrow.
Relief for Seniors, Disabled Homeowners, and Disabled Veterans
Exemption Program
Homeowners who are at least 61 years old, retired because of a disability, or veterans with an 80 percent or greater service-connected disability rating may qualify for a property tax exemption that reduces or eliminates certain obligations.8Washington State Legislature. RCW 84.36.381 – Exemptions – Residences of Senior Citizens and Persons Retired by Reason of Physical Disability The exemption applies to excess (voter-approved) levies, and the benefit depends on household income.
Household income must fall below an annually adjusted threshold set as the greater of the prior year’s threshold or 75 percent of the county median household income. Cowlitz County publishes the current figure on its exemption page, and the Washington Department of Revenue maintains a statewide table at dor.wa.gov.9Cowlitz County, WA. Senior and Disabled Persons Tax Exemption You must also own and occupy the home as your primary residence for at least nine months of the year. Apply through the Assessor’s office with proof of age or disability and income documentation. Once approved, the exemption stays in place unless your income, ownership, or occupancy changes.
Deferral Program
A separate program lets qualifying homeowners postpone taxes rather than reduce them. You can defer taxes on up to 80 percent of your equity in the property.10Washington State Legislature. RCW 84.38 – Deferral of Special Assessments and Property Taxes You must be at least 60 or retired because of a disability, with qualifications similar to the exemption program though income requirements may differ.
Deferred taxes are not forgiven. They become a lien on the property and accrue interest at 5 percent per year until paid.11Washington State Legislature. RCW 84.38.100 – Lien of State – Amount – Priority The balance comes due when you sell the home, move out, or pass away. If your mortgage lender holds a lien on the property, they may need to cosign the deferral declaration. This program fits homeowners who need to stay put now and have enough equity to cover the eventual payoff.
Appealing Your Assessed Value
If you believe the Assessor set your value too high, you can appeal to the Cowlitz County Board of Equalization. The deadline is July 1 of the assessment year or 30 days after the date your value change notice was mailed, whichever is later.12Cowlitz County, WA. Board of Equalization13Washington State Legislature. RCW 84.40.038 – Valuation of Property – Appeal to Board of Equalization This is not the same as the tax payment deadline. You still owe the tax while the appeal is pending.
The Board only considers whether the assessed value reflects actual market value. It will not adjust levy rates or dollar amounts. To win you need evidence the Assessor got the value wrong:14Cowlitz County, WA. Value Disputes
- Recent sale prices of comparable properties in your area that support a lower value.
- Property conditions the Assessor may not have known about, such as soil that will not percolate, structural damage, or land unsuitable for building.
- Any documentation showing a gap between the assessed value and what the property would actually sell for.
A useful first step is requesting copies of the comparable sales the Assessor relied on. If those comparables are a poor match for your property, that becomes part of your argument. Appeal petition forms are available on the Board of Equalization’s page.
If You Own a Business or a Mobile Home
Property tax in Cowlitz County reaches beyond land and buildings, and two groups have separate rules worth knowing.
Businesses must file an annual personal property listing covering tangible assets like equipment, furniture, machinery, and fixtures. For 2026, listing forms were mailed in late January, with completed forms due by April 30, 2026, to avoid penalties.15Cowlitz County, WA. Business Personal Property If you own a business and did not receive a form, do not assume you are exempt. Call the Personal Property Department at 360-577-3010 ext. 0-6921 to confirm your filing obligation.
Mobile homes are assessed each January 1 like other property, but moving or selling one triggers special rules.16Cowlitz County, WA. Mobile Homes If the home stays put, current-year taxes are payable on the regular schedule. Moving within Washington requires paying the advance tax year (next year’s taxes) before the move. Moving out of state requires only the current year’s taxes. Any move needs a $20 movement permit from the Treasurer’s office, which covers the property tax certification. Selling or transferring ownership requires a Mobile Home Excise Tax Affidavit and proof of a Washington title, and excise-exempt transfers still carry a $10 minimum processing fee.