Newark is a city in Alameda County, California, United States. It was incorporated as a city in September 1955. Newark is an enclave, surrounded by the city of Fremont. The three cities of Newark, Fremont, and Union City make up the Tri-City Area. Its population was 42,573 at the 2010 census making it the third largest city in the US named Newark after Newark, Ohio and Newark, New Jersey.