Of the more than 35,000 person arrested in Illinois each year for DUI offenses, less than fifteen percent are third offenders. The vast majority of these third offenders are men between the ages of 21 and 35. Considering that Illinois has no look-back period, any DUI in Illinois will count as a prior if you are arrested again. A third DUI is treated as a Class 2 Felony, whereas the first two offenses are Class A misdemeanors (unless there was bodily harm).
Administrative penalties are the "paper" part of the process. They do cripple your ability to drive, but they do not limit your physical freedom. These are the punishments that come with the offense:
A threat of jail time accompanies the third DUI conviction. It is a Class 2 felony. A judge only has the option to offer probation as an alternative. This means that there is no avoiding a form of incarceration or personal limitation.
A DUI stays on your record for life. So if you had a first DUI 20 years ago, the subsequent DUI is the second.
There is a distinct difference between the two classifications in Illinois. A felony has mandatory jail time of at least 1 year. Whereas a misdemeanor can carry jail time, it is not a requirement of the punishment. As stated above, a third DUI is automatically a Class 2 Felony.
There are only two options for pleas on a DUI: Guilty or not guilty. Pleading guilty makes for much harsher penalties for the offender. Using a not guilty plea usually results in a lighter sentence. Keep in mind that a DUI offender does not have to blow as it is a constitutional right to not self-incriminate. This combined with a not guilty plea tips the odds in the offender's favor.
Because of the severity of the penalty, it's advisable that you consult with an Illinois lawyer skilled in DUI defense.