The territory remained a French possession until after the French-Indian war when it was ceded to the British by the Treaty of Paris in 1763. British domination of the area ended in 1778 when George Rogers Clark captured Kaskaskia and Cahokia (cities on the southwestern border of Illinois - see map below) and the land was claimed by the Commonwealth of Virginia. After the signing of the Articles of Confederation, Virginia surrendered all claim to the territory to the federal government.

There were many plans advanced for dealing with the new territories. Thomas Jefferson wanted Illinois divided into three states with Kane County in the state of Assenisipia. It was decided, however, to give Illinois large boundaries at the advice of James Monroe who had made several trips to the area and deemed the entire midwest "worthless and uninhabitable."

The Northwest Territory was established in 1787 by Congress to provide for government of all land northwest of the Ohio River. In 1800 Illinois became a part of the Indiana Territory and in 1809 the Illinois Territory was established by an act of Congress. Finally, in 1818 Illinois was admitted as the 21st state with Kaskaskia as its capital.