Siskiyou is one of the 58 counties in the state of California. It was created in 1852 from parts of Shasta and Klamath counties. As of the 2010 census the population was 44,900, up slightly from 44,301 in 2000. The county seat and largest city is Yreka. The county covers 6,347 square miles (16,440 km2), of which 6,287 square miles (16,280 km2) is land. It is bordered by Modoc County in the east, Shasta and Trinity counties to the south, Humboldt County to the southwest, Del Norte County to the west, Josephine County, Oregon to the northwest, and Klamath County, Oregon and Lake County, Oregon to the north.