For statistical purposes, the United States Census Bureau has defined Douglas City as a census-designated place (CDP).

The prehistoric residents of the area were Wintun people; from North Fork to Douglas City the group was called Tien-Tien which means "friends".

[5][6] The explorer Jedediah Smith and his party came through the Hayfork area in 1828, killing several local people to intimidate the others and permit their passage.

[9] Settlers arrived quickly, workings began on other bars in the area and towns formed at places along the trails for housing and supply.

Trinity Sheriff William H. Dixon and a number of men set out to catch the individuals (thought to be Wintu Indians) who killed a well-liked local butcher by the name of J. R. Anderson.

The posse never found the assailants of Anderson, but after two days of tracking, did find another (and much larger camp) of Wintu Indians at the natural bridge.

[11]: 285  In 1863 locals formed the Douglas City Rifles to combat the Wintun; none of their raids caused bloodshed.

[11]: 303–308  In 1859, Theodore Eldon Jones (later the first Trinity County Superior Court Judge) started the short-lived Douglas City Gazette newspaper.

[11]: 296  Renamed Trinity Gazette, it stopped publishing in 1861 as people left the area for the American Civil War and new gold diggings in Idaho.

According to the United States Census Bureau, the CDP covers an area of 25.1 square miles (65 km2), 99.95% of it land and 0.05% of it water.

Pleistocene deposits near Douglas City have Mammoth, Ground sloth and deer fossil bones.

[37] Federally, Douglas City is in California's 2nd congressional district, represented by Democrat Jared Huffman.