Dennis Steven Callahan, 81, of Florham Park, passed away peacefully on January 15, 2026, surrounded by his loving family.

Dennis Steven Callahan was born August 12th 1944 at Mary Immaculate Hospital in Jamaica, New York. Dennis was brilliant and began his IT career at the age of 12 working with computers at Columbia University, having received a research grant from the National Science Foundation. He initially planned to be a research mathematician and began his college career at MIT, where he met his cherished wife; marrying after just knowing each other just a few months. Their story continued and both have said they could never have imagined the life they had or the immense love they felt for each other, he was devoted to her. Dennis had a passion for travel and saw the world along with his wife and children, taking them to places they could only imagine. He loved purely taking care of those around him. He helped enrich many lives, quietly donating to causes close to his heart. He was a man of great faith and left this world knowing that he would be held in the Lords embrace. He will be missed more than words can express.

Beloved husband of over 60 years to Evelyn (Mansfield) Callahan.  Devoted father of Dorothy Callahan, her husband Ed, Laura Callahan, Amanda Harrington and her husband Bryan.  Cherished grandfather of Ellie, Kieran and Savannah.  Proud great-grandfather of Evelyn Rose.  Also survived by many nieces, nephews, cousins and friends.  Dennis was pre-deceased by his parents Lawrence and Dorothy Callahan.

Visitation at the Leonardis Memorial Home, Inc., 210 Ridgedale Avenue, Florham Park on Wednesday, January 21st from 4-7pm.  Funeral on Thursday, January 22nd, assembling at the funeral home at 9:30am, followed by the funeral service at Grace Episcopal Church in Madison at 10:30am.  The funeral service can be viewed livestream by visiting www.gracemadison.org

In lieu of flowers, donations can be made in Dennis's name to www.NourishNJ.org .

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