William Ward Duffield (November 19, 1823 – June 22, 1907) was an executive in the coal industry, a railroad construction engineer, and an officer in the Union Army during the American Civil War.

He graduated in 1842 from Columbia College, New York City, as a civil engineer, and two years later received a Master of Arts.

When the Civil War erupted, Duffield joined the 4th Michigan Infantry as its lieutenant colonel, and participated with the regiment in the First Battle of Bull Run.

Gen. Thomas T. Crittenden, was attacked and defeated by Confederate General Nathan Bedford Forrest in the First Battle of Murfreesboro.

At noon the same day he was made prisoner by General Forrest, but, in his then helpless condition, was released upon his parole promising not to bear arms against the Confederate States until being regularly exchanged.

He was appointed by President Grover Cleveland as Superintendent of the United States Coast and Geodetic Survey, holding that position from 1894 to 1897.