St. Mary of the Immaculate Conception Church in Delavan, Illinois, was established in 1867.  The first church was built on the northeast corner of Second and Cedar streets on land donated by James and Margaret Hayes-Ryan.  The first parish house stood on Fourth Street near Locust.  The second parish house was built on Cedar Street across from the first church.

The current church was built in 1906 and dedicated on May 5th, 1907, under the direction of Rev. A. A. Stapleton, Pastor and the Most Rev. E. M. Dunne, Bishop of Peoria.  Final cost of the church, as stated in 1911, was $18,570.13.  A credit balance of $102 was set aside for a new residence to be built later.  That was built in 1910.  Funds to build the church came from Catholic and non-Catholic donations, 1905-1909 Thanksgiving Festivals, a 1906 chicken supper, and a 1906 Winkel party.

The church was renovated and remodeled in 1959 and the chime system was added.  The basement was excavated in 1961 to house the parish center.  As a result of Vatican II, the interior underwent major renovation in the 1970's including a new altar with the priest facing the congregation, removal of the statues, new pews, new Stations of the Cross, and carpeting.  The latest renovation was in the late 1990's by Deprato Rigali Studios of Chicago.