John S. Folk (c. 1811 – June 25, 1885) was an American law enforcement officer in New York City during mid-to late 19th century.

Folk worked as a carpenter prior to joining the borough's first organized police force, the Brooklyn City Watch, during the 1830s.

He remained "a trusted member" of the city watch throughout his service and, according to the New York Times, his "large and powerful frame, his undaunted courage, and his ceaseless energy made him a valuable preserver of public peace".

[1] The city watch was then composed of officers whose members were elected and, within a short time, Folk was nominated as Head Constable.

After helping stabilize Uptown Manhattan, he joined with Inspector Daniel C. Carpenter to relieve the besieged defenders of the New York Tribune office.

A special meeting of NYPD police captains was held shortly afterwards, which included Superintendent Campbell and Inspector John MacKellar, to appoint a committee to handle the funeral arraignments.

One of his sons, William H. Folk, was a noted veteran police detective and captain of the Twelfth Precinct at the time of his father's death.