Dr. William Linn McMillen (October 18, 1829 – February 8, 1902) was an American surgeon, army general, farmer and carpetbagger legislator.
Born in Hillsboro, Ohio, and educated there, he graduated from Starling Medical College in 1852, and practiced medicine in Ohio until July 1862. McMillen served as a surgeon with the Russian Army in the Crimean War. On the outbreak of the American Civil War, he served as a surgeon with the 1st Ohio Volunteers in 1861, and as Surgeon General of the State of Ohio, 1861-2. He enlisted in the 95th Ohio Volunteer Infantry Regiment serving as colonel. He was wounded on August 30, 1862, in the Battle of Richmond. Accused of cowardly conduct during that engagement (in which he and about half the Union forces involved were captured), he was court-martialed, tried and acquitted after his release.
He led his brigade at the Battle of Nashville. After the Confederate General Thomas Benton Smith surrendered and had been disarmed during the engagement, McMillen reportedly berated the disarmed prisoner and then attacked General Smith with Smith's own sword (one source says "wantonly and repeatedly"), causing brain injuries sufficiently severe that Smith spent most of the rest of his life in a nearby state hospital for the insane. McMillen was brevetted as a brigadier general in 1865, retroactive to the date of the battle, and commanded the district after Robert E. Lee's surrender.
In July 1867, he was brevetted Major General of U.S. Volunteers, retroactive to March 13, 1865. In Smith's obituary, it was stated that when McMillen's role in Smith's injuries became public knowledge, he was asked to relinquish his office in the New Orleans chapter of the Grand Army of the Republic.
McMillen moved to Louisiana in 1866, and began planting cotton. A Republican, he served as a member of the 1868 Constitutional Convention, and as a state senator from 1870–2. In 1872 and 1873 he was elected as a U. S. senator by the McEnery "rump" legislature, but was not admitted to that seat. He served as postmaster of New Orleans under Rutherford B. Hayes, and as Surveyor of the Port of New Orleans under Benjamin Harrison.
He married Elizabeth I. King, née Neil, of Columbus, Ohio on April 18, 1861. Upon his retirement, he returned to Ohio; he died and was buried in Columbus's Green Lawn Cemetery.