The 31st District consists of all or part of Beach Park, Gages Lake, Grandwood Park, Grayslake, Green Oaks, Gurnee, Hainesville, Libertyville, Lindenhurst, Long Lake, Old Mill Creek, Round Lake, Round Lake Beach, Round Lake Heights, Round Lake Park, Third Lake, Venetian Village, Wadsworth, Waukegan, Winthrop Harbor and Zion.

Mary Edly-Allen represented the 51st House district in the 101st General Assembly; she has now been elected to the Senate. She has a B.A. in Education from Northeastern Illinois University and a master's degree in curriculum and instruction with bilingual certification from National Louis University. She is the assistant director of adult education at Mundelein High School, and teaches night classes to English language learners.She also co-founded of an educational nonprofit called Foundation46, and was a founding member of her school district's diversity committee. She is active in many Lake County community organizations, and has served on the board of the Illinois Science Olympiad.