51-year-old Roy Chelsen of Engine 28 in Manhattan is credited with saving dozens of lives on September 11, 2001.
The crowd was so large the service was held at Warwick Valley High School.
After he saw the south tower collapse, he returned to the north tower to help evacuate firefighters.
Chelsen stayed at ground zero, and spent weeks digging through the rubble.
He was later diagnosed with incurable bone marrow cancer.