Lancaster is a charter city in northern Los Angeles County, in the Antelope Valley of the western Mojave Desert in Southern California, United States. As of the 2020 census, the population was 173,516, making Lancaster the 158th-most populous city in the United States and the 31st most populous in California. Lancaster is a twin city with its southern neighbor Palmdale; together, they are the principal cities within the Antelope Valley region.