Belmont in Hawaii

Honolulu MSA includes all of Oahu

Urban Honolulu Metropolitan Statistical Area (MSA) covers the same area as the City and County of Honolulu, which includes the entire island of Oahu and the (uninhabited) Northwestern Hawaiian Islands (except Midway). The census definition of a Metropolitan Statistical Area is that it contains at least one core urban area of 50,000 or more inhabitants.

NOTE: Islands are not a separate census geographic level

Oahu CDPs (Census Designated Places)

Hawaii is the only state where the U.S. Census Bureau does not report data for “incorporated places” (or more commonly “cities”), although legally, the City and County of Honolulu is an incorporated city. Instead, the Census Bureau, through an agreement with the State of Hawaii, recognized the 151 “census designated places” (CDPs) as “places” for data reporting purposes. Had the City and County of Honolulu been recognized as an “incorporated place”, census geography rules would have precluded the reporting of sub‐county data, such as that for East Honolulu, Ewa, Mililani, etc. 

No longer a single "Honolulu CDP" Honolulu Census Designated Place (CDP) was separated in 2010 into 3 areas – Urban Honolulu CDP, East Honolulu CDP and a portion placed in the already existing Hickam CDP.

Hawaii State Data Center guides