The southern end of Puget Sound is the homeland of several indigenous Coast Salish groups, including the Nisqually, Squaxin, and Upper Chehalis.

[7] Permanent European (and later American) settlement of modern-day Thurston County began with the arrival of a pioneer party led by Michael Simmons and George Bush in 1845.

Several families settled near Tumwater Falls at a site they named "New Market", which became the first European settlement in Western Washington.

[9] Thurston County was created on January 12, 1852, by the Oregon Territorial Legislature and Olympia was designated as its seat.

[8] It included the entire Olympic Peninsula and Puget Sound region up to the northern border with British North America and went as far east as the Cascade Mountains.

[8] Olympia was retained as capital of Washington after it was granted statehood in 1889; the city did not win a majority in the first referendum after Ellensburg and North Yakima, but defeated both in a second vote.

Local residents built a branch line to connect with the Northern Pacific Railroad and approved a harbor-dredging operation to promote Olympia as a trade hub as the area fell behind Seattle and Tacoma in population growth.

The modern Washington State Capitol commenced construction in 1923 and was completed in 1928 alongside a campus of government buildings and monuments.

Several state government agencies had attempted to move their offices to Seattle until a 1954 Washington Supreme Court ruling mandated that their headquarters remain in the Olympia area.

[7] The first section of Interstate 5 built in Thurston County was the 6.5-mile (10.5 km) Olympia Freeway, which opened in December 1958 to bypass the city's downtown.

Other sections opened over the following decade, extending access through Lacey and Tumwater, where it destroyed portions of the historic downtown;[12] a proposal to build the freeway further away from Olympia was rejected to preserve rural areas.

[13][14] The completion of Interstate 5 enabled the growth of bedroom communities around Thurston County, which saw its population rapidly increase from the 1950s to 1970s.

The plant was placed on the Endangered Species list in 1997 but due to conservation efforts the 12 in (30 cm) tall prairie flower was delisted in 2023.

From 2010 to 2020, the county's population became more ethnically diverse, with the number of residents who identify as Hispanic or Latino increasing by 63.2%.

[27] Thurston County is also part of the Seattle–Tacoma, WA Combined Statistical Area, which includes most of the Puget Sound region.

Thurston County participates in the Point In Time Count (PTC), a census of the homeless population.

The census allows the county to coordinate with various local, state, and national agencies as an effort to combat homelessness.

Indie label K Records and the Evergreen State College's radio station KAOS, both founded by musician Calvin Johnson, brought many groups into the mainstream and wider success.

[49] The Nisqually Valley News, founded in 1922, is published weekly in Yelm and has been a sister publication of The Chronicle of Centralia since 1994.

[59] Thurston County is a founding member of the Timberland system, which was established as a pilot project in 1964 and made into a permanent intercounty rural library district in 1968.

[60][61] The oldest public library in the county was opened in 1896 by the Woman's Club of Olympia, who donated their collection of 900 books to the city government in 1909.

[62] Thurston County is bisected by Interstate 5, the major north–south freeway on the U.S. West Coast that connects Washington, Oregon, and California.

[63] The freeway travels through Grand Mound, Tumwater, Olympia, and Lacey and continues south to Portland, Oregon, and north to Tacoma and Seattle.

[12] Interstate 5 intersects several other highways within Thurston County that provide connections to other areas of Washington state.

Intercity Transit has 18 routes that serve the cities and urban growth areas of Olympia, Lacey, Tumwater, and Yelm.

[66][67] All routes in the Intercity Transit system have been fare-free since 2020; the agency is funded by a local sales tax within its service area, which was formed in 1980.

[68][69] Rural Transit is operated by the Thurston Regional Planning Council between communities south of Olympia and Tumwater.

[70] Passenger rail service through Thurston County is operated by Amtrak, which has two routes that serve Centennial Station in southern Lacey, which opened in 1993 and is primarily run by volunteers.

[72][73] These routes run on tracks owned by the BNSF Railway, which primarily operates freight trains through the county on the Seattle Subdivision.

[79][80] The Capital Medical Center in Olympia, operated by MultiCare Health since 2021, has 107 beds and an off-campus emergency room in Lacey.