High Quality Content by WIKIPEDIA articles! "Half Moon Bay" redirects here. For the geographical feature in California, see Half Moon Bay (California). For other uses, see Half Moon Bay (disambiguation). Half Moon Bay is a coastal city in San Mateo County, California, USA. Its population was 11,842 as of the 2000 census. Immediately at the north of Half Moon Bay is the Pillar Point Harbor and the unincorporated community of Princeton-by-the- Sea.