Part of the reason that memories of Civil War in Memorial Day observances are not as keen in western Iowa as they are in the eastern part of the state is that settlers here was likely more preoccupied with attacks by the Santee.
Fort Defiance was built in response to those attacks, and though it was never attacked, it did provide a refuge for settlers as the 1862 Sioux uprising swept like prairie fire across southern Minnesota.
Following is a history of the Northern Border Brigade, established for protection of settlers during the 1862 Sioux uprising. The history is taken from the Iowa National Guard website.
Interestingly, one of the blockhouses mentioned in the article still exists in Peterson, a great example of a prairie fort during the 1860s. The blockhouse is just south of the road leading into Peterson from the east.
The Northern Border Brigade
In 1862, only five years after the Spirit Lake Massacre and one year after federal troops were pulled from the frontier to fight in the Civil War, the Santee Sioux went on the warpath in southern Minnesota, near the northern border of Iowa. Five thousand people fled after 600 settlers were killed and 100 women and children were captured by the Indians. With only 91 soldiers of the Sioux City Cavalry available to protect the entire western and northern borders of the state, Governor Samuel Kirkwood authorized the formation of a "Northern Border Brigade" and a chain of forts along Iowa's northern border with Minnesota.
The new brigade was to consist of six troops of cavalry. Each troop was authorized a strength of not less than 40 and not more than 80 men. Each man volunteering was to furnish his own horse and equipment. Two hundred and fifty men were mustered and formed cavalry troops in Sioux City, Denison, Crawford County, Fort Dodge, Webster County and Spirit Lake-Chain Lake.
After formation, the new units, made up of untrained citizen soldiers, moved north to build a fortified line along the state's northern border and to convince the settlers to return to their abandoned farms. Getting people back to their farms was of paramount importance, as Union troops battling the Confederacy needed huge quantities of food. Under these circumstances, every Union farmer was important. Blockhouses or stockades were built at Correctionville, Cherokee, Peterson, Estherville, Chain Lake and Spirit Lake.
These fortifications were built of wood or sod. In Spirit Lake, they built a fort by encircling the brick courthouse with a wooden stockade. The entire chain of fortifications was completed by June of 1863.
September of 1863 saw the routing of the Santee Sioux in the Dakota Territory by Union troops under General Sully. With the need for frontier protection ended, the Northern Border Brigade's mission was complete. The 1864 Adjutant General's Report notes that the Northern Border Brigade had been disbanded.