An NYPD lieutenant — described by family members as a “tough cookie” with “a heart of gold” — has died of a 9/11-related illness, the Daily News has learned.

Marci Simms, 51, died Thursday at her Long Island home, 16 months after she was diagnosed with stage 4 lung cancer.

The Brooklyn-born officer contracted the disease after toiling at Ground Zero for more than four months, her relatives said.

She joined the department in Aug. 1998 after graduating from John Jay College of Criminal Justice.

Simms worked out of Manhattan and Brooklyn before eventually joining the 107th Precinct in Flushing, Queens, in May 2013.

Simms was among the thousands of first-responders who reported to the smoldering site for recovery and clean-up efforts.

“The dust was powdery soft, the air was gray and when I would breathe it in I could feel my throat burning,” Simms was quoted as saying in an online story by Stony Brook University School of Journalism student Brendan Jones.