The death of Capt. George Turner Jr., 60, was confirmed on the department's website over the weekend and by his family Monday.
The family declined to comment further and the department did not respond to several telephone calls and emails for comment.
While the department did not give a cause of death, the firehouse.com website said it was "an apparent heart attack."
Turner, a former data center supervisor with KeySpan, had served with the fire departments in Locust Valley, Glenwood and Glen Cove before joining the Jericho department eight years ago, the department said on its website.
He was elected captain of the department's Trident Engine Co. No. 3 in December 2012 and had been the department's top responder for several years, the department's web posting said.
A funeral Mass will be celebrated at 10 a.m. Tuesday at St. Paul the Apostle Church, 2534 Cedar Swamp Rd., Brookville. Cremation will be private.