The Costa Mesa Historical Society was formed in 1966 as a support group for a historical landmark, the Diego Sepulveda Adobe. This early nineteenth century structure had been given to the City of Costa Mesa by the Segerstrom family with the understanding that it would be restored as a museum for the benefit of the community.

The Costa Mesa Historical Society is collecting, cataloguing and preserving historical data and artefacts pertaining to Costa Mesa and Orange County. The materials are used for research and for public exhibits. We are building collections relating to schools, businesses, churches, civic organizations, people and the World War II Santa Ana Army Air Base.

The purpose of the Society, as stated in our bylaws, is to "promote and preserve the natural, civil, literal, and ecclesiastical history of the Harbor area in general and the City of Costa Mesa in particular." To fulfill this broad purpose, it was planned that the Society would have a building besides the Diego Sepulveda in which to carry out projects, store artifacts, and conduct meetings. Originally, the plan was to build this facility in Estancia Park. But the restoration of the adobe proved too costly, and the plan had to be shelved. So as the Society's collections grew, storage was relegated to private homes and garages.