The area along the Grand River in the northwest corner of present-day Chariton County was first explored by two sons of Daniel Boone and Thomas Stanley prior to Missouri statehood in 1821.

[5] Other than the trading post not much existed in the area for several years, partly due to marshlands and flooding on the Grand River.

[7] Once teeming with wildlife such as prairie chicken, turkey, duck, and deer in the 1800s, the population of such was drastically reduced by over hunting and draining of the native wetlands, notably Hog Lake in 1911.

[5] In 1937 concerned over wetland preservation in the wake of the Dust Bowl, the U.S. Congress established the Swan Lake National Wildlife Refuge just to the south of Sumner.

[5] Roads, buildings and man-made wetlands were soon created by the Civilian Conservation Corps and by 1941 eight hundred geese wintered in the area.

[5] Located on a migratory flyway, Swan Lake and the Sumner area began to attract ever larger numbers of geese in the mid and late 20th century, reaching 100,000 or more by the 1980s and 1990s.

[5] This also led to a yearly influx of hunters, benefiting the few Sumner businesses and Chariton County as a whole.

[8] Sumner also began to hold a yearly Goose Festival in 1955 and it continues each October, with a variety of activities held including live music, a queen contest, food and a parade.

[9] Sumner residents commissioned a Kansas City sculptor in 1976 to create a large statue to honor the community's status and reputation for waterfowl hunting.

[10] According to the United States Census Bureau, the city has a total area of 0.23 square miles (0.60 km2), all land.