10 ILCS 5/29C-15
To determine which group of Legislative Districts shall be the "First group", "Second group", or "Third group" for the purpose of establishing the terms for which Senators shall be elected in each group until the next decennial redistricting, as provided in Section 3 of Article IV of the Illinois Constitution of 1970, the Secretary of State, in the presence of the President and Minority Leader of the Senate, after due notice to them, shall, as soon as practicable after each redistricting finalized according to law, draw one card at random, from 3 cards bearing the numbers 1, 2 and 3, and then draw one card at random from the 2 remaining cards. The first number so drawn shall be the first number of the "First group" and Senators shall be elected from districts in that group for terms as provided in Section 29C-10 for that group. The second number so drawn shall be the first number of the "Second group" and Senators shall be elected from districts in that group for terms as provided in Section 29C-10 for that group. The number on the remaining card shall be the first number of the "Third group" and Senators shall be elected from districts in that group for terms as provided in Section 29C-10 for that group.
10 ILCS 5/29C-15