Coos County was created on Dec. 22, 1853, from parts of Umpqua and Jackson Counties. It was named after a local Indian tribe, the Coos.

Coos County is in southwest Oregon. It is bounded by Douglas County on the north and east, by Curry County on the south, and the Pacific Ocean on the west. Boundary adjustments with Curry County in 1855 and 1872 and Douglas County in 1882, 1951 and 1983 resulted in the present county which has an area of 1,629 square miles.

In January 1854, the Territorial Legislature established Empire City as the county seat. In 1895 the legislature permitted the citizens of the county to choose a new county seat. The 1896 vote resulted in the designation of Coquille City as the new county seat.

The first county courthouse was built in Empire City. The first courthouse in Coquille was erected in 1898. An addition, referred to as the "hall of records," was built in 1916. In 1951 the old courthouse was torn down. The "hall of records" was left standing, and in 1951 and 1953 east and west wings were added at the cost of $180,000 and $260,000 for each wing.

The government of Coos County consisted originally of a county probate judge, two county commissioners and a sheriff. The office of county clerk was first an appointive and later an elective office. Other early offices included the county school superintendent, county treasurer, and county assessor. The county court was replaced by a board of commissioners in 1961.

The first census in 1860 showed a population of 445. The 2013 population of 62,860 represented a 0.3% decrease from the 2010 population.

Although exploration and trapping in the area occurred as early as 1828, the first settlement was established at Empire City in 1853. The Territorial Legislature granted permission for the development of wagon roads from Coos Bay to Jacksonville in 1854 and to Roseburg in 1857. Although a mountainous county, it has areas suitable for agriculture and dairy farming. Timber and fishing are the foundation of the county's economy. The area also produces large quantities of shellfish.

There are several port districts in the county: Port of Coos Bay founded 1909, Port of Coquille River founded 1912, and Port of Bandon founded 1913. Coos Bay is considered the best natural harbor between San Francisco Bay and the Puget Sound. 

Gold mining drew people to explore and exploit the mineral resources of the county during the 19th century. Today there are rich deposits of iron ore, lead and coal that await development. Vacation and recreational possibilities, such as golf courses, the Oregon Dunes National Recreation Area, and many state parks, attract tourists and provide an economic stimulus.