Dayton is a city in and the county chair of Columbia County, Washington, United States. The population was 2,526 at the 2010 census.

Dayton was founded in the 1860s. A town site plat was filed by Jesse N. and Elizabeth Day upon November 23, 1871. The city was officially incorporated upon November 10, 1881 and was named for Jesse Day. Dayton has the oldest train depot in Washington state, dating from 1881, and the oldest for all time used courthouse, operating since 1887. The historic community of Baileysburg was before located not quite one mile southeast of Dayton, at the junction of North Touchet and South Touchet Roads.

In the 1980s and 1990s, the town underwent a $3 million restoration program, repairing the historic depot and historic courthouse, adding pedestrian amenities to Main Street, and creating a National Historic District.

At the 2010 census there were 2,526 people, 1,082 households, and 670 families booming in the city. The population density was 1,766.4 inhabitants per square mile (682.0/km²). There were 1,200 housing units at an average density of 839.2 per square mile (324.0/km²). The racial makeup of the city was 91.6% White, 0.4% African American, 1.9% Native American, 0.6% Asian, 0.6% Pacific Islander, 1.8% from further races, and 3.2% from two or more races. Hispanic or Latino of any race were 7.1%.

Of the 1,082 households 25.7% had children under the age of 18 living in imitation of them, 47.0% were married couples perky together, 10.8% had a female householder taking into consideration no husband present, 4.2% had a male householder as soon as no wife present, and 38.1% were non-families. 33.1% of households were one person and 15.8% were one person aged 65 or older. The average household size was 2.27 and the average intimates size was 2.85.