William L. Hadden (October 8, 1896 – July 11, 1983) was an American politician who was the 87th lieutenant governor of Connecticut from 1943 to 1945.

He was also Assistant Clerk of the Town Court of West Haven from 1919 to 1921, Prosecuting Attorney from 1923 to 1927 and judge from 1927 to 1937.

He was elected Lieutenant Governor of Connecticut in November 1942 together with Republican gubernatorial candidate Raymond E. Baldwin.

He served for one two-year term from January 6, 1943, but while Baldwin was reelected in 1944, Hadden was not and was replaced with Democrat Charles Wilbert Snow.

Hadden was appointed Attorney General of Connecticut by Baldwin in 1945, to fill the vacancy caused when Francis A. Pallotti resigned to become a judge.