Lancaster is a charter city in northern Los Angeles County, in the Antelope Valley of the western Mojave Desert in Southern California. As of the …Lancaster is a charter city in northern Los Angeles County, in the Antelope Valley of the western Mojave Desert in Southern California. As of the 2020 census, the population was 173,516, making Lancaster the 153rd-most populous city in the United States and the 30th 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.