Waipahu is a former sugarcane plantation town and now census-designated place (CDP) located in the ʻEwa District on the island of Oʻahu in the City & County of Honolulu, Hawaiʻi, United States. As of the 2020 census, the CDP population was 43,485. The U.S. postal code for Waipahu is 96797.

Honolulu County, officially known as the City and County of Honolulu, is a consolidated city-county in the U.S. state of Hawaii. The city-county includes both Urban Honolulu and the rest of the neighborhoods on the island of Oʻahu, as well as several minor outlying islands, including all of the Northwestern Hawaiian Islands except Midway Atoll.