The above videos are a superb overview of Illinois politics during the Civil War. Illinois has always been a state divided politically. During the Civil War, Republicans controlled the northern part of the state by and large, and by and large the Democrats controlled the southern part of the state, with central Illinois being a battleground between the parties. The Republicans were the champions of the War, while the Democrats, with exceptions, tended to be against the War and in favor of a negotiated peace. Draft resistance was wide spread in southern Illinois, and the state was rife with copperhead (Southern) sympathizers. Go here to read a good brief history of Illinois copperheads.
On March 28, 1864, political passions turned violent in Charleston, Illinois with nine men dead and twelve wounded. Read about it here.
Illinois contributed more than a quarter of a million men to the Union army and navy, the third most of any state. It is sobering to think what might have happened if open civil war had broken out in the State. Although passions were white hot, this did not occur, but as the Charleston riot indicated, history might easily have taken another path.
Victory in the War also meant that the Republicans swept to power in Illinois in the 1864 election. However, neither of the political parties in Illinois have yet been able to hold the reigns permanently in their hands, and the Republican tenure in power, while it went on for almost three decades, did not alter the divided nature of Illinois politics.