It was named for John Edgar,[3] an Irish-born officer in the Royal Navy who resigned rather than fight against the Americans in the Revolutionary War.

Edgar moved to Kaskaskia, Illinois, in 1784, becoming a miller and merchant in that town.

Two are operated by CSX Transportation and the third by the Eastern Illinois Railroad Company.

[9] As of the 2010 United States Census, there were 18,576 people, 7,839 households, and 5,148 families residing in the county.

There were 8,803 housing units at an average density of 14.1 per square mile (5.4/km2).

It has been carried by only two Democrats since 1940 – Lyndon Johnson in 1964 by just 139 votes, and Bill Clinton in 1992 by a 41.1 percent plurality.