Geo quick facts: San Clemente Island is the southernmost of the Channel Islands of California. It is owned and operated by the United States Navy, and is a part of Los Angeles County. It is administered by Naval Base Coronado. Defined by the United States Census Bureau as Block Group 2 of Census Tract 5991 of Los Angeles County, California, it is 21 miles (34 km) long and contains 147.13 km2 (56.81 sq mi) of land. The island is officially uninhabited as of 2000 U.S. Census. It is estimated, however, that the number of military and civilian personnel present on the island at any given time is at least 300. The city of San Clemente in Orange County, California is named after the island – wikipedia.