The Union Church of San Salvador traces its beginning to 1942 when Earl and Inez Terzian, a couple from the U.S., provided Sunday School to their children at home. Soon, other families asked to join them and interest developed in establishing an English-speaking congregations. The first worship service was held on July 7, 1946.

In 1974, work began on the church's permanent home in Colonia La Mascota. The first service was held there on May 11, 1975 From the time of its organization to the present, thousands of people from all over the world have been a part of the Union Church's community of faith. The UCSS has been served by 21 pastors from a variety of denominations.