Colusa (formerly, Colusi, Colusi's, Koru, and Salmon Bend) is the county seat of Colusa County, California. The population was 5,971 at the 2010 census, up from 5,402 at the 2000 census.
According to the United States Census Bureau, the city has a total area of 1.8 square miles (4.8 km²), all of it land. According to the United States Geologic Survey, the city's location is at 39°12′52″N 122°00′34″W / 39.21444°N 122.00944°W / 39.21444; -122.00944.
Colusa is on the Sacramento River, which has a high levee so that the river is not clearly apparent from the city.