Randolph County was organized in 1795 out of a part of St. Clair County.
It was named in honor of Edmund Randolph, Governor of Virginia.
George Rogers Clark of the army of Virginia captured the area from the British on July 4, 1778, near the end of the Revolutionary War.
The area then became the seat, for several years, of Illinois County, Virginia, although the Congress of the Confederation legislated the existence of the Northwest Territory on July 13, 1787.
 Edmund Randolph was Governor of Virginia at the time Virginia ceded the Northwest Territory to the United States.
 In 1809, when Illinois became a separate territory, Territorial Secretary Nathaniel Pope, in his capacity as acting governor, issued a proclamation establishing Randolph as one of the Illinois' two original counties.
 The county's boundaries were last changed in 1827, when land was taken to form Perry County.

The Mississippi River has played a prominent role in the county's history, altering its boundaries in 1881 when it severed the isthmus that connected Kaskaskia to the Illinois mainland, destroying the original village of Kaskaskia and forcing its historic cemetery to be relocated across the river to Fort Kaskaskia.
 Crains Island , southeast of Chester, is another enclave of Illinois west of the Mississippi that was created by a change in the river's course.
Randolph County was organized in 1795 out of a part of St. Clair County. It was named in honor of Edmund Randolph, Governor of Virginia. George Rogers Clark of the army of Virginia captured the area from the British on July 4, 1778, near the end of the Revolutionary War. The area then became the seat, for several years, of Illinois County, Virginia, although the Congress of the Confederation legislated the existence of the Northwest Territory on July 13, 1787.  Edmund Randolph was Governor of Virginia at the time Virginia ceded the Northwest Territory to the United States.  In 1809, when Illinois became a separate territory, Territorial Secretary Nathaniel Pope, in his capacity as acting governor, issued a proclamation establishing Randolph as one of the Illinois' two original counties.  The county's boundaries were last changed in 1827, when land was taken to form Perry County.
The Mississippi River has played a prominent role in the county's history, altering its boundaries in 1881 when it severed the isthmus that connected Kaskaskia to the Illinois mainland, destroying the original village of Kaskaskia and forcing its historic cemetery to be relocated across the river to Fort Kaskaskia.  Crains Island , southeast of Chester, is another enclave of Illinois west of the Mississippi that was created by a change in the river's course.
Randolph County, Illinois