Seal Beach is located in the westernmost corner of Orange County. To the northwest, just across the border with Los Angeles County, lies the city of Long Beach and the adjacent San Pedro Bay. To the southeast are Huntington Harbour, a neighborhood of Huntington Beach, and Sunset Beach, also part of Huntington Beach. To the east lie the city of Westminster and the neighborhood of West Garden Grove, part of the city of Garden Grove. To the north lie the unincorporated community of Rossmoor and the city of Los Alamitos. A majority of the city's acreage is devoted to the Naval Weapons Station Seal Beach military base.

Early on, the area that is now Seal Beach was known as "Anaheim Landing", as the boat landing and seaside recreation area named after the nearby town of Anaheim. The site of Anaheim Landing is now registered as a California Historical Landmark.

By the 20th century, it was known as Bay City, but there was already a Bay City located in Northern California. When the time of incorporation on October 27, 1915, the town was named Seal Beach. The town became a popular recreation destination in the area. The Joy Zone, a beach-side amusement park built in 1916, was the first in Orange County.

The United States Navy's Naval Weapons Station Seal Beach was originally constructed during World War II for loading, unloading, and storing of ammunition for the Pacific Fleet, and especially those US Navy warships home-ported in Long Beach and San Diego, California. With closure of the Concord Naval Weapons Station in Northern California, it has become the primary source of munitions for a majority of the U.S. Pacific Fleet.

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