The Board of County Commissioners is the County's legislative authority and is made up of three commissioners elected to four-year terms. The county is divided into three districts based on population and at the time of election each Commissioner must live in and represent his/her district. The Commissioners are partisan and are nominated in a primary election embracing only their particular district. All voters in the county are given an opportunity in the general election to select the commissioner who will ultimately serve.

Under the rules devised by each board, the commissioners meet at such frequency and at such locations as deemed necessary, and a chair is elected to preside over these meetings. Thurston County Commissioners meet every Tuesday at 2:00 p.m. in Room 280 of the County Courthouse. If Tuesday is a holiday, the meetings are cancelled for the week.

One of the County Commissioners' primary duties is to levy the taxes to operate the county and to adopt a balanced budget for each calendar year. The Commissioners fix the budget amount for each department of the county, but variances and increases can be permitted during the year if a need can be shown. Other elected officials in the county are responsible for their own adopted budget and the County Commissioners are responsible for the operation of budgets under the control of appointed department heads.

Also within their legislative capacity, the Commissioners are responsible for adopting, amending and repealing all county ordinances (which are essentially laws of the county). These include traffic, zoning, planning and public safety ordinances, and any other ordinance concerning the general welfare of the county.

As administrators, Thurston County Commissioners have appointed a Chief Administrative Officer who is responsible for following through with Board direction for:

	Public roads and public works programs
	Public health services
	Planning and zoning of unincorporated areas
	Emergency services or civil defense programs
	County park and recreation systems
	Other services and programs which are not clearly the responsibility of another elected county official

The Commissioners have a key role in a wide variety of community boards and commissions that affect citizens within and even beyond their jurisdictions. Commissioners often serve on a variety of multi-county boards (such as library and health), with other public officials, to direct public policy. Within the county structure, they are also responsible for adopting members of county boards and commissions (such as parks and planning).