Washington County - The Provisional Legislature created Washington County as Tuality District on July 5, 1843, as one of the four original counties created in Oregon. Tuality County was bordered on the north by latitude 54deg. 40min., on the east by Clackamas County, on the west by the Pacific Ocean, and on the south by Yamhill County. In 1844, the Columbia River was made the northern boundary of Tuality County and Clatsop County was created from Tuality County's western half. In 1849, the Territorial Legislature changed the name of Tuality County to Washington in honor of President George Washington. Washington County obtained its present boundaries in 1854 with the creation of Columbia County to the north and Multnomah County to the east. The area of Washington County is 727 square miles.

Columbia was selected as the county seat in 1850. Later, the town was given the name of Hillsborough, which in 1858 was modified to Hillsboro. After meeting in two local church buildings, a permanent county headquarters was built in 1852. A brick courthouse was built in 1873 and remodeled in 1891. In 1912 an annex was built. A new courthouse was built in 1928 to replace the original brick structure. The Justice Services Building was added on to the courthouse in 1972. The Public Services Building was constructed in 1990 to house offices of the clerk, assessor, surveyor, planner, and human services.

Although Tuality County government was established in 1843, a complete county government was not organized until 1845 when three county judges having probate and administrative authority, a treasurer, and a sheriff were appointed. The first election of county and territorial officers was held in 1846. County business was conducted by the county court from 1845 to 1851 when the organization of the county court was changed to consist of three elected commissioners.

The voters of Washington County approved a home rule charter at the general election in 1962. The new county government was headed by the county administrative officer and board of county commissioners, which is the policy determining body of the county.

Washington County is one of the fastest developing areas in Oregon with a population of 445,342 in 2000. That represents an increase of 42.94% since 1990. The development of a large electronics industry during the last two decades has contributed significantly to the economy of the county. Other principle industries are agriculture, lumber, manufacturing, and food processing.