The eight islands are split among the jurisdictions of three separate California counties: Santa Barbara County (four), Ventura County (two) and Los Angeles County (two). The islands are divided into two groups — the Northern Channel Islands and the Southern Channel Islands. The four Northern Islands used to be a single landmass known as Santa Rosae.

Santa Catalina Island is the only one of the eight islands with a significant permanent civilian settlement—the resort city of Avalon, California, and the unincorporated town of Two Harbors.