Because Democrats have a supermajority — 40 members to 19 Republicans — the real voting will take place in a secret, closed-door meeting of the Democratic caucus scheduled for 11 a.m.
Once — or if — a senator secures 30 votes, the entire Senate will convene to elect the new president.
So far the top contenders are state Sens. Kimberly Lightford of Maywood and Don Harmon of Oak Park, though in the end someone else could get the nod.
Current Senate President John Cullerton is retiring after more than a decade in the role.
Because of how rare these sorts of openings are in Illinois, the competition is expected to be fierce.