10 ILCS 5/20-2.3
Any member of the United States Armed Forces while on active duty, and his or her spouse and dependents, otherwise qualified to vote, who expects in the course of his or her duties to be absent from the county in which he or she resides on the day of holding any election, in addition to any other method of making application for vote by mail ballot under this Article, may make application for a vote by mail ballot to the election authority having jurisdiction over his or her precinct of residence by a facsimile machine or electronic transmission not less than 10 days before the election.
Ballots under this Section shall be delivered by the election authority in the manner prescribed by Section 20-5 of this Article in person, by mail, or, if requested by the applicant and the election authority has the capability, by facsimile transmission or by electronic transmission. Ballots voted under this Section must be returned postmarked no later than election day and received for counting at the central ballot counting location of the election authority during the period for counting provisional ballots, the last day of which is the 14th day following election day.
10 ILCS 5/20-2.3