St. Paul is a small town in northern St. Charles County and consists its namesake Catholic church, the church picnic grounds, school, several ballfields associated with the church and school, as well as a Knights of Columbus hall. It no longer has the part-time Post Office, the accounting office, real-estate office, and city office in one small building remain however. There is a volunteer fire station for the O'Fallon Fire Protection District. There is also an auto repair shop and the semi-famous Dog Prairie saloon. Local lore states that St. Paul was once named Dog Prairie.
St. Paul neighbors O'Fallon to the southeast, Old Monroe to the northeast, and Josephville, Flint Hill, and Wentzville to the west. St. Paul is above the Mississippi River floodplain and consists of rolling hills that are mainly formed by various water features. It has a mix of residential and agricultural land..