Signal Hill is a small city (2.2 mi², 5.8 km²) in Los Angeles County, California that is an enclave (completely surrounded by the city of Long Beach). As of 2005, the city population was 10,951. The city was incorporated on April 22, 1924, roughly three years after oil was discovered on Signal Hill. The city once shared three different postal ZIP codes with Long Beach, but in July 2002, the City of Signal Hill received its own ZIP code, 90755. It is in the 562 area code.