St. Barnabas was founded by Irish immigrants who moved to the Mazomanie area to build the Milwaukee & Mississippi Railroad. They initially came as Mazomanie was platted by the railroad in June 1855 and within a year the Congregation was established. The first wooden church may have been built as early as 1857, in the lot in front of the present stone building. Fifty families founded the congregation. It grew to 74 families by 1890. The construction of the present church building began in 1889 and was finished within a year. In 1929 a fire destroyed the church, but it was reconstructed with the same walls. There were 312 families of 1100 persons in 1974. Today the parish consists of 384 families of 810 persons.