Dave O'Neal. He was elected with Big Jim Thompson in '76 and reelected in '78 (when they switched to the off-year elections). I'm forgetting if it was he or his predecessor, Neal Hartigan, that was the first to win the job on a ticket elected with the Governor (remember Dem Paul Simon won Lt Gov even as Republican Dick Ogilvie won the Governorship in '68). O'Neal thought he was going to win the open Senate seat in 1980 when Adlai Stevenson the 3rd retired (in anticipation of running for Governor in '82). When he failed and it went to Sec of State Alan Dixon (one of the few Dem successes in the Reagan landslide), he had nowhere to go. Thompson made it plain he wasn't going to step aside in '82, so O'Neal just quit in July '81 and left the office vacant for a year and a half. I don't think anyone much noticed. Of course, that then gave then-House Speaker George Ryan his opportunity, and he managed to serve a whole 8 years in the job. When he was succeeded by Bob Kustra in '91, Kustra was the anointed choice for Senator in '96, but after he was upended by Al Salvi in the primary, he eventually quit early, too, in July of '98.
I would prefer they keep the office around (New Jersey's past is proof of how awkward the suddenly transfer of power is without a Lt. Governor), but give it some teeth. I think everyone can agree that it would have been better to have Pat Quinn preceding over the state senate than Emil Jones. I agree with Impy they have a procedure in place to name an acting Lt. Governor in the event of a vacancy too. I think in a few states, like Texas, the Lt. Governor post is arguably more powerful than the Governor. I wouldn't go that far, but Illinois certainly should at least give the job similar clout as Vice President, and perhaps a few more actual powers than Joe Biden has under the U.S. Constitution. (perhaps a provision that the Governor & Lt. Governor meet once a week to discuss the affairs of government... this would have forced Blago to keep Quinn in the loop about the state budget)
Neal Finkelman, a Gurnee conservative, says that he was the lt. gov., July 1998-Jan. ‘99. He must have been appointed by then-Gov. Edgar.