The Illinois fought back but, no match for the powerful Iroquois, soon settled for a strategy of assimilation with the French, leaving central Illinois and relocating their villages near the Mississippi River trading posts and missions, practicing agriculture and livestock-raising, and intermarrying with soldiers and settlers. Gradually, disease, alcoholism, and cultural disintegration reduced the Illinois people to the pitiful existence of "trading-post Indians." By the close of the eighteenth century, the Illinois had all but lost a unique tribal identity. (13)

Sugar Creek: Life on the Illinois Prairie (1986)
John Mack Faragher