William F. Cassidy (August 28, 1908 near Nome, Alaska – March 31, 2002) was a commanding officer in the United States Army during and after World War II.

During World War II Cassidy commanded engineer troops specializing in airfield construction in England, North Africa, and Italy.

He served as South Pacific Division Engineer from 1955 to 1958 and was the senior logistics advisor to the Republic of Korea Army in 1958–59.

Cassidy was the Corps' Director of Civil Works from September 1959 to March 1962 and was then appointed Deputy Chief of Engineers.

Other military decorations included the Legion of Merit with Oak Leaf Cluster, the Bronze Star and the Republic of Korea Presidential Unit Citation.