The discovery of Kennewick Man along the banks of the Columbia River provides evidence of Native Americans' settlement of the area for at least 9,000 years.

[8] American settlers began moving into the region in the late 19th century as transportation infrastructure was built to connect Kennewick to other settlements along the Columbia River.

While Hanford and Pacific Northwest National Laboratory continue to be major sources of employment,[9] the city's economy has diversified over time and Kennewick today hosts offices for Amazon and Lamb Weston.

[17] Ranchers began working with cattle and horses in the area as early as the 1860s, but in general settlement was slow due to the arid climate.

[28][9] Due to activity at the Hanford Site, the 1950 census recorded major population growth in the Tri-Cities, with Richland overtaking to become the largest city in the region.

[29] An effort to build a new bridge began in 1949 and was funded in 1951 because of increasing traffic between Kennewick and Pasco, largely due to commuters heading to and from the Hanford Site in Richland and McNary Dam, which was under construction near Umatilla, Oregon.

The two-lane Green Bridge was the only one for automobiles across the Columbia River in the Tri-Cities at the time, and the 10,000 cars crossing it daily had created traffic problems.

[34] In 1963, regional NAACP leaders started pressuring the state government to investigate exclusionary practices and staged demonstrations in front of city hall.

[35][36] Initial meetings led the state to determine that while no official policy banning African Americans from the city existed, racial discrimination was a significant barrier to that community living and feeling safe.

[40] Higher accumulations were recorded in surrounding communities, such as Ritzville, and the ash plume was thick enough to trigger street lamps to turn on at noon.

[44] Oregon eventually opposing proposed routes that didn't cross the Umatilla Bridge, a compromise was reached placing I-82 on its current alignment to the south and southwest of Kennewick while authorizing the construction of Interstate 182 as a spur heading directly into Richland and Pasco.

A 2015 genetic analysis confirmed the ancient skeleton's ancestry to the Native Americans of the area (some observers contended that the remains were of European origin).

[50] Kennewick fared better than most of the state during the Great Recession, primarily due to consistent job growth in the metro area during that time.

[57][58] The nearest eruptive vent to Kennewick from this period is near Ice Harbor Dam along the Snake River upstream of Burbank and Pasco.

The pressure from the resulting lake would periodically build to the point that the dam would fail, sending massive amounts of water cascading to the Pacific Ocean.

[62] Should the next earthquake occur, damage is expected to be minimal in and around Kennewick, but destruction west of the Cascades could have a major impact of the economy of inland areas.

[65] The Cascades create an effective rain shadow, causing Kennewick to receive a fraction of the precipitation that cities west of the mountains like Portland and Seattle get annually, with values being more similar to that of Phoenix, Arizona.

[69] Floods like this were the result of melting snow, and were most extreme when a heavy snowpack developed in the mountains over winter followed by a strong regional heatwave.

[70] Zintel Canyon Dam located near the Southridge Sports and Events Complex was built to protect parts of the city from a 100-year flood.

While the creek that flows through Zintel Canyon typically runs dry, summer thunderstorms in the Horse Heaven Hills can generate destructive flash floods.

High pressure combining with the low angle of the sun in winter brings stability in the atmosphere, allowing denser cold air to sink to the floor of the Columbia Basin.

[73] If a weather system drops precipitation but isn't strong enough to clear the inversion, freezing rain or sleet can fall in Kennewick.

These events can happen any time of the year but is most common in the spring and fall months when farms in the region have high amounts of exposed soil.

[77][78] Summer brings extreme heat and low humidity, which are ideal conditions for wildfires in undeveloped areas adjacent to town.

[96] Irrigation enhanced the region through further diversification of agricultural products coming from the Columbia Basin to include vineyards and a variety of vegetables and tree fruit.

In higher elevations, like much of the Horse Heaven Hills, there is no access to irrigation water, limiting agricultural activities in that area to ranching and growing wheat.

[99] Recently, industrial growth in Hermiston and at the Port of Morrow in Boardman has led to an increase in the number of Kennewick residents who commute to those areas for work.

[107] Benton and Franklin Counties combine to host a single fair at the end of each summer at the fairgrounds off SR 397 in east Kennewick.

[147][148] In the early 2010s, the city built the 52 acres (21 ha) Southridge Sports and Events Complex in the quickly growing south end of town along US 395.

[150] Kennewick was able to secure a piece of the World Trade Center from the Port Authority of New York and New Jersey, which is located in the southeast corner of the complex as a memorial to the victims of the September 11 attacks in 2001.