The first mission station established in the county was in 1857 at Anamosa. Monticello belonged to this mission. At this time there were but few Catholics in Monticello, but many more came in 1858 and 1859, to assist in the construction of the Dubuque & Southwestern Railroad. Prior to 1868 services were held in Kinsella Hall and in what was known as Davenport's Hall on the second floor of the old Monticello State Bank building.
In 1868, Rev. Father Cogan established the parish in Monticello and was its first resident priest. He built a frame structure in the southern part of town which was known as the Church of the Sacred Heart. The following is a partial list of the names of the heads of families of the parish: Michael Breen, Cornelius Brown, Henry Burrows, Andrew Burns, Patrick F. Cunningham, Patrick Cushing, John Fleming, John Farley, Daniel Kinsella, Edward Kinsella, Mrs. Ella McMahon, John Mathews, Madam McCormick, John McConnell, Andrew Munday, Patrick OToole, Michael Quirk, Robert Shane, Mrs. Peter Young.
In 1871, Rev. Father Cogan was succeeded by Rev. Father David Welch who made his residence in Monticello for a short time, and then moved to Castle Grove, but still had charge of the parish here. The roof was blown off the little frame church, which was re-roofed by Father Welch. This church was thirty feet by sixty.
In 1872, Rev. P. O. Dowd, now of Petersville, Iowa, took charge of the parish of Castle Grove, with Monticello as an outside mission, and remained until the year 1878, when on October 8 the church was destroyed by a tornado that swept the southern portion of the town.
The following Sunday, the members met at a little vacant schoolhouse in the northern part of the town, and on December 14 of the same year, Very Reverend P. J. O'Connor, a young and zealous priest came and took up the work of rebuilding the church, with Sand Spring as an outside mission. It was at this time that courage was needed for it seemed that the congregation was diminishing instead of increasing, but the pastor erected the present church and parochial residence, the comer stone of which was laid in 1880.
From the time the church was destroyed by the tornado in 1878, until the present church was finished in the fall of 1880, services were held in the old schoolhouse. Along with the work of building and trying to pay the debt on the church, Father O'Connor gave his attention to the instruction of a large Sunday school. About the year 1884 Father O'Connor was succeeded by Rev. J. Tobin, who remained nearly four years. During his stay he made some improvements to the church property and continued the work already begun by Father O'Connor in the Sunday school. In 1887 Father Tobin was removed to Fairbanks, Iowa.
About Christmas, 1887, Rev. J. McCormick came to reside in Monticello., and has remained ever since. He is a man ever kind and sympathetic to those in trouble, distress and sickness. Being a progressive age improvements have continued to be made on the church and property until nearly twenty thousand dollars have been expended, and now the church and residence are among the finest and most up-to-date church properties in the county.