St. Ansgar is a city in Mitchell County, Iowa, United States.

[3] St. Ansgar is named for the patron saint of Scandinavia, a French Benedictine monk who Christianized much of Denmark, Sweden, and northern Germany between 830 and 865 A.D.

The St. Ansgar church, congregation, and town served as a center for the dispersion of Norwegian immigrant settlers north across the border into Minnesota and into western Iowa from the mid-1850s into the late 1870s.

According to a booklet published by the First Lutheran Church of St. Ansgar on the occasion of the 150th anniversary of the congregation, the church, which is made of limestone quarried from the banks of the nearby Cedar River and native hardwoods, is the oldest continuously active Lutheran church west of the Mississippi River.

Pastors in the Church of Norway received university training in census record-keeping; the parish keeps copies of congregation records continuously from founding to the present, making them a significant genealogical resource.

A fortified stone outbuilding locally called Fort Severson, 5.5 miles northwest of St. Ansgar near Carpenter, Iowa, was built in 1867 by settlers associated with the Clausen settlement anxious about the continued presence of Dakota Indians traveling through the area along the Deer Creek and the Cedar River.

The distinctively fortified building, which functioned both as a barn and a fort, is the sole surviving example of many that were built.

[4] According to the United States Census Bureau, the city has an area of 1.03 square miles (2.67 km2), all land.

31.4% of all households were made up of individuals, and 18.2% had someone living alone who was 65 years of age or older.

34.0% of all households were made up of individuals, and 22.1% had someone living alone who was 65 years of age or older.