In Office: We can accept checks or cash in office. During closed or busy office hours, you can use the drop box located outside of the Treasurer's Office doors, drop boxes located at the North and South entrance of the Administration Building and a Drive up drop box in the North Parking Lot of the Administration Building located at 207 4th Ave. N, Kelso. By Mail: Send a check in to: Cowlitz County Treasurer 207 N 4th Ave Kelso, WA 98626 By Credit Card: Please visit http://www.co.cowlitz.wa.us/index.aspx?NID=1874 or call 1-844-965-0200. Credit/debit card payments are also acceptable in the Treasurer's Office. All checks must be made payable to Cowlitz County Treasurer. If the payment coupon is not included please be sure to include the parcel number or property id. Your payment must be postmarked by the due date to be considered timely, otherwise interest and/or penalty will apply RCW 01.12.070.