Under present Illinois law, it does not matter if the DUI occurred on private property or on a public roadway. Being on private property does not exempt a prosecution for DUI.
When a person is charged with DUI, the prosecution must prove certain elements beyond a reasonable doubt. Generally, to carry the burden of prosecution at trial, the government must show the following: 1) That person was driving a vehicle or in actual physical control of said vehicle; and 2) That at the time the person drove a vehicle he/she was under the influence of alcohol, any drug or other drugs, or some combination of both that rendered the person incapable of driving safely. The prosecution does not have to prove that a person was on a specific road or highway as an arrest on private property at the time of the offense also qualifies.
This is because The DUI statute does not specify that a person has to be on a public roadway or highway or on private property in order to be in violation of the statute. Under Illinois law, there is no requirement that a DUI violation must occur on a public roadway or highway in order to be enforceable and under that same principle being on private property is also not a requirement. In short, being on private property does not constitute a defense to the charge of DUI. However, being on private property can be used as a defense against a Statutory Summary Suspension that would normally follow a DUI arrest. The Statutory Summary Suspension can only be invoked if the DUI offense occurred in a public area.
It is very clear that if the legislature wanted to carve out an exception to the DUI statute with regards to the issue of private property then it would have done so by now. For contrast, compare the DUI statute with the language that governs the offense of Driving While License Suspended or Revoked. Under the statute for Driving While License Suspended or Revoked, the law specifically mandates that a person who drives or is in actual physical control of a motor vehicle while on “any highway" occurring when a person’s driver’s license or permit is revoked or suspended will be found guilty of such an offense. Under the offense of Driving While License Suspended or Revoked, being on private property is a proper and useful defense to this particular charge especially if the officer never observed the person driving on any road or highway.