The first court sessions in Washington County were held in the Presbyterian and Methodist meetinghouses in 1846-47. Court was first convened on the present courthouse site in 1850 when a log building on a quarter section of land was purchased from David Hill. To honor this man, the name of the small settlement was then changed from Columbia to Hillsborough (this name was shortened to 'Hillsboro' in 1858).In 1852, a two-story courthouse, built of native pine and cedar, was erected here. Then, in 1873, the wood-framed structure was replaced by a brick building in the Italianate style. A clock tower was added in 1891 and an annex was built in 1912.
The current Neoclassical courthouse, featuring fluted Ionic columns, full entablature with lions' heads and Greek-inspired ornamentation on the roof line, was built in 1927-28 and incorporated the 1912 addition to the earlier structure.
The champion sequoias at the south end of the building were placed to enhance the entrance of the 1873 courthouse and were three years old when they were planted in 1880 by pioneer nurseryman John Porter. Porter had brought the seeds back from his Gold Rush days in California.
