Skip to main content


May contain: clothing, hat, garden, nature, outdoors, adult, male, man, person, people, gardening, soil, accessories, formal wear, tie, gardener, plant, and vegetation


In 1957, the Washington State legislature passed Revised Code of Washington (RCW) 17.28 – Mosquito Control Districts. This legislation allows for the creation of Mosquito Control Districts and provides guidance and authorities associated with the operation of a District. The primary reason that a Mosquito Control District is formed is for the welfare of the public.

Benton County Mosquito Control District #1 was formed in 1957, but funding and operations did not begin until 1969/1970. The formation of this District was brought about due to a concern for repeated epidemics of encephalitis like those seen in the 1940s and to a lesser extent, the 1950s.

Benton County is listed as having 22 different mosquito species and Yakima County has 36 different species (provided by WA Dept of Health). The District has physically trapped 16 different species of mosquitoes. Some of these species are vectors (an organism that can transmit pathogens) for diseases, like West Nile virus (WNv), St. Louis Encephalitis (SLE) and Western Equine Encephalitis (WEE).

Originally, Benton County MCD consisted of the city of West Richland and county lands surrounding the areas of Benton City, Kennewick, and Richland. The city of Richland was annexed into the District in 1970. The cities of Prosser and Benton City were annexed in 1971. In 1990, areas of the city of Kennewick that were not within the District were annexed. The District expanded even more in 1992 with the annexation of Grandview and Mabton.

We are governed by a Board of Trustees that is comprised of appointed representatives from each of the cities and county commissioner districts within the District. This works out to 7 city representatives and 5 county commissioner representatives; 3 for Benton County and 2 for Yakima County.


Funding is generated by a special assessment that is levied against real property within the District.  The following information is explanatory in nature, for the actual wording of the resolution, please contact the District office.

In Benton County, the following considerations are applied:

  • Properties within the District are classified as "unimproved" or "improved" by the County Assessor.  This determination is not made by the Mosquito Control District.
  • Accurately assessing the specific benefit of mosquito abatement operations to individual properties is extremely difficult, highly subjective and prone to uncontrollable variables (e.g., weather or fluctuating river levels).
  • Personal Property will not be assessed.
  • Federal and State-owned properties will not be assessed.
  • Properties labeled as exempt due to "Senior/Disabled" or "U500" will not be assessed.
  • Improved properties larger than 0.25 acres often require resources above and beyond routine operations, such as aerial or truck-mounted spraying to prevent and control mosquito populations.
  • Properties designated as multi-unit will have an additional fee assigned.

Benton County

For 2024, the assessment is as follows:  Unimproved properties shall be assessed a flat rate of $8.00 per property.  Improved properties shall be charged a rate of $40 per acre up to the first 0.25 acres of land, and $0.50 per acre for any acreage over the first 0.25 acres. The remaining assessment amount will be equally divided amongst improved properties, that are subject to the benefit assessment, to determine a flat rate per property (approximately $29.76 for 2024).

Example #1; a single improved property with 0.6 acres would be charged:

  • The flat rate for an improved property, subject to the assessment, of $29.76,
  • plus the $40 per acre rate, up to the first 0.25 acres, or, $10.00 ($40/acre x 0.25 acres = $10),
  • plus the $0.50 per acre rate, for the additional 0.35 acres (in excess of the first 0.25 acres), or, $0.18 ($0.50/acre x 0.35 acres = $0.18),
  • for an approximate total of $39.94 ($29.76 + $10.00 + $0.18).

Example #2; a single unimproved property with 5 acres would be charged:

  • $8.00 flat rate for the unimproved property (acreage does not matter IF the parcel is unimproved, so, there would not be any acreage rate).


Yakima County

For 2024, the assessment is as follows:  A flat rate of $24.95 per property and a $5.91 per acre rate.

Example #3; a property (i.e., parcel) consisting of 1 property with 0.8 acres would be charged:

  • The flat rate for a property of $24.95,
  • plus the $5.91 per acre rate for the 0.8 acres, or, $4.73 ($5.91/acre x 0.8 acres = $4.73),
  • for an approximate total of $29.68 ($24.95 + $4.73).

The District appreciates that these numbers, or the process, may be a bit confusing.  We are glad to explain this further and try and answer any questions that you may have.  Please do not hesitate to contact us.