Colleagues, family and friends of the young aspiring police officer gathered at a Sunday afternoon service at Absegami High School in Galloway Township, New Jersey.
Dozens of uniformed firefighters were lined up in the parking lot ahead of the service to pay their respects.
Besides volunteering at the fire department, Natalie Dempsey, the older sister to three brothers, worked at the Humane Society of Atlantic County, her mother said.
"She loved animals and loved helping people," Natalie Dempsey's mother, Stacey Dempsey, wrote to ABC News Wednesday. "Her ultimate goal was to become a K-9 officer."
"She also found true love in her boyfriend, Andy. He was her soulmate and best friend," Stacey Dempsey said. "She loved music, all music. But her favorite was Christmas music. Her favorite holiday.
"She loved Christmas movie marathons. She sang Christmas music all year long," she added. "She had such a wit about her. Sarcasm at its finest. Always making people laugh. Not a day went by that you didn’t see her bright smile."
Fellow firefighter Tiffany Platt agreed, describing Natalie Dempsey's smile as "infectious."
"This is a family, and we lost a member," Platt told ABC News Wednesday. "She just wanted to help people. It was who she was. It was what she wanted to do."