Dempsey was a New Jersey native with an "infectious" smile, Dempsey's fellow firefighter, Tiffany Platt, told ABC News on Wednesday.
Besides working as a volunteer firefighter, Dempsey was also studying to become a police officer, Platt said.
"She wasn't done," Platt said. "She just wanted to help people. It was who she was. It was what she wanted to do."
Dempsey was pronounced dead on the scene and was the only one in the car, WABC reported. Her car was only found after her own fire company stopped to assist other officials at the accident scene when returning from the initial fire to which Dempsey was reporting.
The Mays Landing Fire Department, which works with the Mizpah volunteer force, responded to the accident. The department called her "vibrant" and "always smiling."
Both companies shared photos of Dempsey, one with a huge smile decked out in full uniform and gear, as well as another where she is playfully posing covered in firefighting foam.
"Please join us in extending our thoughts and prayers to Ms. Dempsey's family as well as to her firehouse family during this tough time," the Mays Landing Fire Department said in a statement. "Natalie Dempsey, thank you for your service; we'll take it from here."
"It's not just a volunteer fire department -- this is a family and we lost a member," Platt said. "We just want everyone to slow down, pay attention, always say 'I love you' when you leave. Because your time is never given."
Mizpah Fire Chief Jay Davenport told NJ.com that Dempsey had just passed the Firefighter 1 certification and had attended the police academy over the summer.
Mizpah is about 25 miles west of Atlantic City, in southern New Jersey.