Mililani sits on former plantation fields owned by Castle & Cooke, which began planning for its development in the early 1960s under its Oceanic Properties subsidiary. Castle & Cooke's plan was to make Mililani Town a satellite city by using a prestigious group of planners and architects to satisfy Oahu's great pent-up demand for housing with a sensitively designed, affordable new community of a type unique in Hawaii. Architect and developer Al Boeke, who would later create the planned community of Sea Ranch, California, was the development director of Mililani. The first homes in Mililani went on sale on June 3, 1968.
In 1976, the Interstate H-2 opened, cutting travel time from Mililani to Honolulu in half. In 1986, Mililani was named an All-America City. It is the only community in Hawaii ever to receive this distinction. Mililani is the third wealthiest zip code (96789) in the state of Hawaii, according to the 2006 ranking by Pacific Business News.
Although it is largely a bedroom community for Honolulu, Mililani has its own commercial shopping centers, schools (such as Mililani High School), parks, community centers, and a golf course, and resembles a modern American suburban town. Mililani homeowners must pay dues to the Mililani Town Association, which enforces covenants and design standards, and provides recreational facilities including several pools.
The older portion of Mililani to the west of Interstate H-2 is known as Mililani Town. The newer portion of Mililani to the east of Interstate H-2 is known as Mililani Mauka. Almost all of Mililani's commercial and retail centers are in Mililani Town. A third region of Mililani is Launani Valley, a secluded, master planned development located below Mililani Tech Park on Wikao Street. The area was developed by Towne and contains a blend of townhome and single family units.
On April 6, 1990, ground was broken for Mililani Mauka, a newer and more upscale community east of the Interstate H-2. The first homeowners moved into Mauka in 1992.
In 2003 Mililani was designated as the pilot site for the City and County of Honolulu's curbside recycling program. In 2005, Money magazine named Mililani as one of the best places to live in the U.S. In 2006, Mililani Ike Elementary School first grade teacher Phyllis Nakama-Kawamoto was named Hawaii's American Star of Teaching by the U.S. Department of Education.