Isaac Stephenson (June 18, 1829 – March 15, 1918) was an American politician of the Republican Party who represented Wisconsin as both a United States Representative and a United States Senator.
He was born in the community of Yorkton, near Fredericton in York County, New Brunswick (now Canada, but a British colony at the time).
His parents were Isaac Stephenson (1791–1874), a lumberman and farmer born in Ireland of Scotch-Irish ancestry, and Elizabeth (Watson) Stephenson (?–1838), who was born in London.