San Luis Obispo (Spanish for Saint Louis of Anjou) is one of the 58 counties in the state of California. The county (commonly abbreviated as SLO, pronounced "slow") was created in 1850, making it one of the original counties of the state. As of the 2010 census, the population was 269,637, up from 246,681 in 2000. The county seat and largest city is San Luis Obispo.
The county has 3,615.54 square miles (9,364.2 km2) of area, of which 3,304.32 square miles (8,558.1 km2) is dry land. SLO is bordered on the west by the Pacific Ocean, on the north by Monterey County, has a tiny border with Kings County to the northeast, is bordered on the east by Kern County and on the south by Santa Barbara County.