David C. O'Neal was an American law enforcement officer and politician who served as the 41st Lieutenant Governor of Illinois from 1977 to 1981. For six years he served as Saint Clair County Sheriff, the first Republican to hold that office in twenty years.

The lieutenant governor of Illinois is the second highest executive of the State of Illinois. In Illinois, the lieutenant governor and governor run on a joint ticket and are directly elected by popular vote. Gubernatorial candidates select their running mates when filing for office and appear on the primary election ballot together. When the governor of Illinois becomes unable to discharge the duties of that office, the lieutenant governor becomes acting governor. If the governor dies, resigns or is removed from office, the lieutenant governor becomes governor. Under the Illinois Constitution, the Attorney General is next in line of succession to the Governor's office after the lieutenant governor, but does not succeed to the lieutenant governor's office. From the impeachment of Rod Blagojevich in 2009, until the inauguration of Sheila Simon in 2011, Attorney General Lisa Madigan would have become governor if Pat Quinn had vacated the office. Historically, the lieutenant governor has been from either the Democratic Party or Republican Party. The current lieutenant governor is Democrat Juliana Stratton.