730 ILCS 5/5-7-8: Subsequent Sentences.

(a) The service of a sentence of imprisonment shall satisfy any sentence of periodic imprisonment which was imposed on an offender for an offense committed prior to the imposition of the sentence. An offender who is serving a sentence of periodic imprisonment at the time a sentence of imprisonment is imposed shall be delivered to the custody of the Department of Corrections to commence service of the sentence immediately.

(b) If a sentence of imprisonment under Section 5-4.5-55, 5-4.5-60, or 5-4.5-65 (730 ILCS 5/5-4.5-55, 5/5-4.5-60, or 5/5-4.5-65) is imposed on an offender who is under a previously imposed sentence of periodic imprisonment, such person shall commence service of the sentence immediately. Where such sentence is for a term in excess of 90 days, the service of such sentence shall satisfy the sentence of periodic imprisonment.