In 1836, King married Ellen Eliot, who died two years into marriage; they had no children. After five years, King married her sister Susan Eliot, and they had two children. His son Rufus King Jr. became a Union Army officer of the U.S. Horse Artillery Brigade and was awarded the Medal of Honor; his other son, Charles King became a Brigadier General of Volunteers during the Spanish–American War and a writer of Western novels.
In 1845, he left New York and moved to the Wisconsin Territory, accomplishing a mixture of politics, journalism, and education. King also organized and played in the first three baseball games played in the state of Wisconsin. The matches were played at the old State Fairgrounds during the winter of 1859.
King was appointed by President Abraham Lincoln as Minister to the Papal States in 1861 after being recommended by the Secretary of State Seward. On his way to Rome when the Civil War broke out, he took a leave of absence to join the Union Army. He was appointed a brigadier general of the Wisconsin militia on April 15, 1861, and of U.S. Volunteers on May 17, and was given authorization to raise a Wisconsin regiment. King helped organize what came to be known as the famous Iron Brigade, the Second, Fifth, Sixth, and Seventh Wisconsin, and Nineteenth Indiana volunteers, which he commanded briefly. However, before the Iron Brigade saw combat, King was promoted on March 13, 1862 to command of a division in the I Corps of the Army of the Potomac replacing general Irvin McDowell. The Division's first action was in the in August 1862. On August 28, 1862, King received orders to advance on Warrenton Turnpike towards Centreville, Virginia. Later in the day, his division was attacked by Confederate forces under Stonewall Jackson's command. Suffering from epileptic seizures, King spent the battle in an ambulance wagon and turned over command of the division to Brig. Gen John P. Hatch, the ranking brigade commander. Hatch then led King's division at Second Bull Run and during the Maryland Campaign until being wounded at South Mountain. In December 1862, King served on the court-martial of Maj. Gen. Fitz John Porter for disobedience and cowardice at Second Bull Run. King performed garrison duty at Fort Monroe, Virginia, and was a military governor of Norfolk. His epileptic seizures became more frequent, and in October 1863, King resigned his commission, and succeeded Richard Milford Blatchford as Minister to the Papal States. He served until the end of 1867, and was instrumental in apprehending John Surratt in Rome.
Postbellum career
Returning to New York from Rome in 1868, King served for two years as deputy comptroller of customs for the Port of New York, but then retired on account of failing health. He quietly lived in retirement until he died in New York City in 1876. He is buried in Grace Churchyard, Jamaica, New York.
