William A. Jayne (October 8, 1826 – March 20, 1916) was an American politician and physician.

He attended Illinois College in 1844 where he was a founding member and served as first president of Phi Alpha Literary Society.

He began his practice in Springfield and served as Abraham Lincoln's personal physician.

He became mayor of Springfield in 1859, and then a member of the State Senate in 1860, but resigned in 1861 to accept the appointment by President Lincoln to be the first Governor of Dakota Territory.

He was appointed U.S. Pension Agent in 1869 for four years and served three terms as mayor of Springfield beginning in 1876.