The St. Isidore Catholic Parish was established in 1921. Parishioners met for services at the local Felts Market or the Harmona Hotel, whichever could accommodate them. In 1922, the parishioners asked the Bixby Land Company for a piece of the land to build a Catholic church.
In 1924, the Bixby Land Company assigned the southwest corner of Church Street and Main Street (now Katella Avenue and Reagan Street) to the Roman Catholic Bishop of Monterey and Los Angeles for the filing fee of ten ($10.00) dollars. The property was used to build the first Catholic church in Los Alamitos. First Pastor assigned to St. Isidore was Father Miguel Santacana when it was built and opened in 1926.
The year 1933 saw much of the building destroyed in the Long Beach earthquake. The parishioners rebuild St. Isidore to its present Spanish Revival architecture style that stands today.
The Orange Diocese closed St. Isidore in 1960 when St. Hedwig Catholic Church was opened on Los Alamitos Boulevard. In 1972, Father Quinn reopened St. Isidore and had the hall built to serve as a family center.
In May, 1999, the Orange Diocese once again closed St. Isidore with the last service being held on the last Sunday of the month, September 26, 1999.
With the closing of the church, a committee of dedicated parishioners and community members formed a non-profit organization to purchase, preserve and protect the St. Isidore site for present and future generations, renaming it the St. Isidore Historical Plaza. The site is now a community center.
The Los Alamitos Museum Association on November 29, 2011, designated the chapel building at St. Isidore Historical Plaza, as the oldest remaining community building in Los Alamitos. The dedicated was held on June 10, 2012.