John Jacob Cohen (20 December 1859 – 25 March 1939) was an Australian politician.
He was born in Grafton to storekeeper Samuel Cohen and Rosetta Manser.
Having also studied architecture at night school, he moved to Mackay in Queensland in 1882 as a consulting engineer and architect, subsequently moving to Brisbane in 1884.
In 1898 he was elected to the New South Wales Legislative Assembly as the National Federal member for Petersham, but by 1901 he was re-elected as a Liberal.
[1] In 1919, he resigned from parliament to become a Judge of the District Court, allegedly as part of a deal between William Holman and the Liberals that had led to the Nationalist government in 1917.