William Jayne (October 8, 1826 - March 20, 1916) was an American physician and stateman. He served as Governor of the Dakota Territory and as the territory's delegate to the United States House of Representatives.
William was born in Springfield, Illinois, and graduated in medicine from the University of Missouri at Columbia in 1849. 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 served from May 27, 1861-1863, then as a Delegate to the House from March 4, 1863 to June 17, 1864.
Jayne returned to Springfield and continued the practice of medicine. He was appointed U.S. Pension Agent in 1869 for four years and served three terms as mayor of Springfield beginning in 1876. He also served as Director and Vice President of the First National Bank of Springfield. He resumed the practice of medicine in 1873.
He married Julia Witherbee in 1850 and had six children with her. He died in Springfield and is interred in Oak Ridge Cemetery in Springfield.