Stephen Wallace Dempsey (May 8, 1862 – March 1, 1949) was an American Republican politician. He was a member of the United States House of Representatives from New York.

S. Wallace Dempsey
Chairman of the Committee on Rivers and Harbors
In office 1921–1931
Member of the U.S. House of Representatives from New York's 40th district
In office March 4, 1915 – March 3, 1931
Preceded by	Robert H. Gittins
Succeeded by	Walter G. Andrews
Personal details
Born	May 8, 1862 Hartland, New York, U.S.
Died	March 1, 1949(1949-03-01) (aged 86) Washington, D.C., U.S.
Resting place	Rock Creek Cemetery Washington, D.C., U.S.
Political party	Republican

Born in Hartland, New York, Dempsey was an assistant United States Attorney from 1899 to 1907. He was a special assistant to the Attorney General from 1907 to 1912 and was in charge of the prosecutions of Standard Oil and certain railroad companies.

In 1914, Dempsey was elected to Congress and served from March 4, 1915, to March 3, 1931.

S. Wallace Dempsey died at age 86 in Washington, D.C. He is interred in Rock Creek Cemetery.