John "Jack" S. O'Brien, 88, a resident of Grayslake, IL, passed away December 27, 2025, at his home. He was born February 4, 1937 in Chicago, IL, to John and Joy Adele (Wilson) O'Brien. 

Jack is survived by his wife of 67 years, Cathryn O'Brien, his children Jeanne (Jack) Lasheff, Debra "Debbie" (Michael) Borsic, Laura (Jack) McClory, John (Carri) O'Brien, and Kelly (Brian) Haeflinger, his grandchildren Connor (Skylar) Lasheff, Tiffany (Chris) Rail, Nora (Micheal) Ramsey, Rebecca Doering, Kevin (Emily) McClory, Ryan (Erin) McClory, Katlyn (Matt) Ivey, and Erin (Landon) Pfeiffer, his 16 great-grandchildren, and his 1 great-great-grandchild, his brothers James O'Brien and Paul O'Brien, his sister-in-law Mary O'Brien, his step-sister-in-law Mary Jane Ryan, and his numerous nieces and nephews.  He was preceded in death by his parents, his brothers Timothy Michael O'Brien and Patrick O'Brien, and his sisters-in-law Linda O'Brien and Jane O'Brien.  

Jack graduated from Mount Carmel High School in Chicago in 1955 and was an avid sports fan his entire life, cheering on the White Sox, Bulls, Bears, and Blackhawks, as well as many high schools associated with his children and grandchildren.

A visitation and funeral mass are scheduled for Saturday, January 10, 2025 at St. Gilbert Catholic Church 301 E. Belvidere Rd. Grayslake, IL 60030 from 10:00am until 11:00am with the mass commencing at 11:00am.  Interment will be held privately.  In lieu of flowers, memorials may be made to Tunnel to Towers, City of Hope Cancer Treatment Center or Lightways Hospice.

All funeral arrangements were entrusted to Strang Funeral Chapel & Crematorium 410 E. Belvidere Rd. Grayslake, IL 60030.  For more information log onto www.strangfuneral.org or contact (847)223-8122.