Horicon National Wildlife Refuge was established in 1941 to provide an undisturbed sanctuary for a number of migratory birds and waterfowl including the redhead duck as well as to provide opportunities for people to connect with nature through many wildlife dependent recreational activities such as wildlife observation, photography, environmental education and interpretation, fishing and hunting. 

Horicon Marsh is a shallow, peat-filled lake bed scoured out of limestone by the Green Bay lobe of the massive Wisconsin glacier. The glacier entered this area about 70,000 years ago and receded about 12,000 years ago. The same layer of rock that forms the gentle hills to the east of the marsh extends 500 miles to the east and is the same rock layer over which the Niagara River plunges at Niagara Falls. This Niagara Escarpment bordering the marsh, commonly referred to as "The Ledge" extends for 230 miles in the state of Wisconsin alone. The marsh itself is approximately 14 miles long and ranges from 3-5 miles in width.

Native people built effigy mounds between 700 A.D. and 1200 A.D. These earthen burial mounds, ranging in size from 25 feet to over 300 feet long, were built to represent animal and geometric shapes including panther, bear, bison, deer, birds and others. These mounds contained many artifacts. The oldest known human artifact in the state of Wisconsin - an 11,200 year-old projectile point - was found near the Ledge in Oakfield, just north of Horicon Marsh. At one time, many more mounds were to be found around the marsh. Many of these, however, have been destroyed as land was converted for other purposes. Many different Native American groups used the marsh - the Ho-Chunk, Potawatomi and Menominee.

European immigrants settled on the south end of the marsh in the 1800's and logging opened the uplands for farming. In 1846, a new settlement called Hubbard's Rapids, at the south end of the marsh, was renamed "Horicon" - which is a Mohican word for pure, clean water. That same year, settlers built a dam on the Rock River in Horicon that changed the marsh into the largest artificial lake in the world at that time - Horicon Lake. People used the lake to float logs and move farm products by steamboat. Water from this dam also powered a saw mill and a grist mill. After the dam was removed in 1869, the lake reverted to a marsh once again. Over the next 30 years, people used Horicon Marsh for unregulated recreational and commercial hunting - critically depleting bird populations. With the marsh depleted of its wildlife, the next phase began in 1910 with the ditching and draining of the marsh for agricultural production (muck farming - onions, potatoes, carrots etc). Soon the farming stopped due to limited success. Since the water was drained away and the heavy soil was tilled, the exposed peat dried and spontaneously combusted into fire. Peat fires raged for years until local citizens (led by Curly Radke of the local chapter of the Izaak Walton League) rallied legislators for the Horicon Marsh Wildlife Refuge Bill of 1927 which provided money to buy the land and build a dam which was finished in 1934 and still is used today to regulate appropriate water levels. In 1941, the federal government purchased the rest of Horicon Marsh, and Horicon National Wildlife Refuge was established on May 9th for the protection and conservation of migratory birds.

The northern two-thirds of Horicon Marsh is managed by the U.S. Fish & Wildlife Service as the 22,000 acre Horicon National Wildlife Refuge. The southern third of the marsh, 11,000 acres, is managed by the Wisconsin Department of Natural Resources as Horicon Marsh State Wildlife Area. At more than 33,000 acres, Horicon Marsh is one of the largest freshwater marshes in the United States and is a critical rest stop for thousands of migrating ducks and Canada geese. It is recognized as a Wetland of International Importance, as both Globally and State Important Bird Areas, and is also a unit of the Ice Age Scientific Reserve.

Located in Dodge and Fond du Lac counties, Horicon Marsh is fed by the Rock River which flows through the refuge, following a course through southern Wisconsin and eventually ending in the Mississippi River at Rock Island, Illinois.

Horicon National Wildlife Refuge is managed as part of a complex that also includes the Fox River National Wildlife Refuge, 1,054 acres in Montello, WI; the Green Bay National Wildlife Refuge, 330 acres, and Gravel Island National Wildlife Refuge, 27 acres, located in Lake Michigan near Washington Island, WI; and the Leopold Wetland Management District, 57 waterfowl production areas, totaling 13,000 acres, located in 17 counties throughout Wisconsin. A total of twenty-two staff work to manage wildlife, habitat, and recreational opportunities on these areas within the complex.