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. Lancaster is located approximately 70 miles (110 km) north (via I-5 and SR 14) of downtown Los Angeles, 9 miles south of the Kern County line. It is separated from the Los Angeles Basin by the San Gabriel Mountains to the south and from Bakersfield and the San Joaquin Valley by the Tehachapi Mountains to its northwest. The population of Lancaster has grown from 37,000 at the time of its incorporation in 1977 to over 173,000 as of 2020.