Sangamon County was formed in 1821 out of Madison and Bond counties.
The county was named for the Sangamon River, which runs through it.
The origin of the name of the river is unknown; among several explanations is the theory that is comes from the Pottawatomie word Sain-guee-mon (pronounced "sang gä mun"), meaning "where there is plenty to eat."
 Published histories of neighboring Menard County (formed from Sangamon County) suggest that the name was first given to the river by the French explorers of the late 17th century as they passed through the region.
The river was named to honor "St. Gamo", or Saint Gamo, an 8th-century French Benedictine monk.
The French pronunciation "San-Gamo" is the legacy.

Prior to being elected President of the United States, Abraham Lincoln represented Sangamon County in the Illinois Legislature.
Lincoln, along with several other legislators, was instrumental in securing Springfield, the Sangamon County seat, as the state's capital.
Sangamon County was also within the congressional district represented by Lincoln when he served in the US House of Representatives.
Another legislator who represented Sangamon County was Colonel Edmund Dick Taylor, also known as "Father of the Greenback".
The prominent financiers and industrialists Jacob Bunn and John Whitfield Bunn were based in Springfield, Sangamon County, Illinois, as well as in Chicago, during the nineteenth century and the early twentieth century.
The careers of these men and the people with whom they collaborated helped to shape much of the history and development of Sangamon County, Illinois.
Sangamon County was formed in 1821 out of Madison and Bond counties. The county was named for the Sangamon River, which runs through it. The origin of the name of the river is unknown; among several explanations is the theory that is comes from the Pottawatomie word Sain-guee-mon (pronounced "sang gä mun"), meaning "where there is plenty to eat."  Published histories of neighboring Menard County (formed from Sangamon County) suggest that the name was first given to the river by the French explorers of the late 17th century as they passed through the region. The river was named to honor "St. Gamo", or Saint Gamo, an 8th-century French Benedictine monk. The French pronunciation "San-Gamo" is the legacy.
Prior to being elected President of the United States, Abraham Lincoln represented Sangamon County in the Illinois Legislature. Lincoln, along with several other legislators, was instrumental in securing Springfield, the Sangamon County seat, as the state's capital. Sangamon County was also within the congressional district represented by Lincoln when he served in the US House of Representatives. Another legislator who represented Sangamon County was Colonel Edmund Dick Taylor, also known as "Father of the Greenback". The prominent financiers and industrialists Jacob Bunn and John Whitfield Bunn were based in Springfield, Sangamon County, Illinois, as well as in Chicago, during the nineteenth century and the early twentieth century. The careers of these men and the people with whom they collaborated helped to shape much of the history and development of Sangamon County, Illinois.
Sangamon County, Illinois