The Journal News said it obtained the database legally through a Freedom of Information Act request after the shootings in Sandy Hook, Conn., that killed 20 children and eight adults.
The Journal News said the posting spread rapidly through social media, with Facebook users recommending the map more than 20,000 times.
The Journal News said hundreds of people have contacted them to complain and argue that posting the database violates the permitholders' privacy and is therefore illegal.
Robert Freeman, executive director of the state Committee on Open Government, said all public records are presumed to be public unless a statute prohibits their release.
CynDee Royle, editor and vice president of The Journal News, stood by her decision.
"We knew publication of the database would be controversial, but we felt sharing as much information as we could about gun ownership in our area was important in the aftermath of the Newtown shootings," she said.