This town was laid out in 1857, and named for Mr. O'Fallon, a well-known capitalist of St. Louis, who at the time was a member of the board of directors of the old North Missouri Railway. Nicholas Krekel, a brother of Judge Arnold Krekel, personally superintended the survey and platting of the village, and Mr. Krekel was appointed postmaster in 1857, and still occupies that office. The first church was built in 1857, it being Assumption Roman Catholic, of which more extended mention is made hereafter. The first public school was opened in 1869, by a Mr. A. Bradley.

A Catholic convent was located here. The institution was a very flourishing one, containing upon an average about one hundred sisters of the society of the "Precious Blood," many of whom were continually engaged in teaching throughout the country districts about O'Fallon. The first Mother Superior was Sister Augustina, who, some years ago went to Europe, being succeeded by Sister Armella. The institute of learning, formerly connected with the convent, has been removed to St. Louis, and no scholars are now instructed at the convent, the commodious brick buildings, erected at a cost of $35,000, being devoted exclusively as a headquarters for the sisters of the order.