Cambodia's Island are generally grouped into 3 locations

Kep's Islands are located off Kep's shore, next to Vietnam in the South-East corner of Cambodia.  Only one island is open for overnight stays.

SihanoukVille's Islands are mostly a few minutes or hours off the coast of SihanoukVille, Cambodia, although the farthest extends out over 100km.  90% of the tourist islands are located here.

Koh Kong's Islands are located close to the shore of Koh Kong City (and Koh Kong Province), right next to Thailand.  This is in the South-West of Cambodia.  The largest island here is also called Koh Kong Island.

Most of the islands are called KOH something.  the KOH, pronounced "GAW", very quickly, means "island" in the Cambodian language of Khmer.