John Guy McDowell (February 25, 1794 in Chemung, then in Tioga County, New York – January 1, 1866 in Chemung, now in Chemung County, New York) was an American politician from New York.
On December 21, 1815, he married Laurinda Lowman (1793–1859), and they had nine children.
He was a member of the New York State Assembly (Tioga Co.) in 1830 and 1831.
He secured the charter for, and was the first President of, the Chemung Canal Bank.
He was also an associate judge of the Tioga County Court for some time.