George Griswold Sill (October 26, 1829 – May 19, 1907) was an American politician who was the 37th Lieutenant Governor of Connecticut from 1873 to 1877.
Sill was born at Windsor, Connecticut. After preparatory studies at Ellington Academy, he attended Yale University from 1848 to 1852 and was a member of Skull and Bones. He studied law and was admitted to the Hartford County Bar in 1856.
When the American Civil War broke out, he organized the first company of Connecticut Volunteers in his office and went to the front.
Sill was also the head of several large firms and corporations, serving as President of the Hartford Governor Company and Director of the Mutual Benefit Life Insurance Company.
After voting Republican from the first vote he could cast, Sill changed parties to the Democrats in 1872, under the leadership of Horace Greeley. In 1873, he was nominated by the Democrats for the election for Lieutenant Governor of Connecticut and won a large plurality. He served in four consecutive one-year terms, while Charles R. Ingersoll was the Governor, from May 7, 1873 to January 3, 1877. These were the last one-year terms, changes in the Connecticut State Constitution made the terms for governor and lieutenant governor two years long from 1877 on, putting the election in November the year before and having the term start in January.
Sill was a U.S. Attorney for Connecticut from 1888 to 1892.
He died at his home on the night of May 19, 1907, following an attack of locomotor ataxia.