Chetlain was born in St. Louis, Missouri. His parents were Swiss, and they came to the United States by the way of Canada. As an infant, he was taken to Galena, Illinois. He studied at local schools in Galena, and later became a clerk. In 1852 he started a career in business, and by 1859, he became wealthy. He sold his business in the U.S. and traveled in Europe. Upon returning, Chetlain participated in the 1860 U.S. presidential campaign.
Civil War service
When the American Civil War began in 1861, Chetlain chose to follow the Union cause. He was said to have been the first man in Illinois to volunteer for the Civil War. On April 16 he was part of a meeting held in Galena to raise a volunteer company, and with Ulysses S. Grant was prominent in its creation. When Grant declined the post Chetlain was elected as the company's captain. In Springfield in late April the 12th Illinois Infantry was organized, and Chetlain's company was added to it. On May 2 he entered the Union Army as captain of the 12th Illinois, and the next day he was elected the regiment's lieutenant colonel. Shortly afterward the 12th Illinois was ordered to Cairo, and that September it was part of the force used by Grant in the expedition against and capture of Paducah. Then Chetlain was given command of Smithland, Kentucky, where he constructed fortifications to defend part of the Cumberland River. In January 1862 he rejoined his regiment, and led it during the expedition up the Tennessee River, was at the capture of Fort Henry on February 6, and led his command during the Battle of Fort Donelson from February 12 to 16. On April 6, 1862, Chetlain led his regiment with distinction during the Battle of Shiloh. In the fight he lost about a quarter of his men, and Chetlain was wounded when both his face and chest were seriously bruised. On April 27 he was promoted to colonel for gallantry during the action at Fort Donelson. That May his command participated in the Siege of Corinth and then the battle there on October 3 and 4, during which Chetlain was again highly praised for his performance. Chetlain was then given command of Corinth, Mississippi, where he began to organize and train black soldiers for Union Army service. This assignment lasted until May 1863, and on December 18 he was promoted to the rank of brigadier general. On the advice of Grant, Chetlain was given the task of raising black troops in Tennessee and Kentucky, with his headquarters located in Memphis. By October 1864 he had trained a force of about 17,000 men that were "well armed, drilled, and disciplined." On June 18, 1865, Chetlain was brevetted to the rank of major general. Between 1865 and 1866 he commanded at Memphis and then at Talladega, Alabama On January 26, 1866, Chetlain was mustered out of the Union Army. His war-time performance has been described as:
Postbellum
After the American Civil War, Chetlain was assessor of Internal Revenue for the district of Utah from 1867–69. From 1869–72, he was at U.S. consul in Brussels. In 1872, he established himself in the banking business in Chicago and also as a stock broker. He was president of the Home National Bank, organizer of the Industrial Bank of Chicago, director of the Chicago Stock Exchange, and member of the Boardof Education. He was also an active philanthropist. He was prominent in the Military Order of the Loyal Legion and the Grand Army of the Republic for many years. In 1893 he wrote Recollections of Seventy Years. On March 15, 1914 he died in Chicago. He was buried in Greenwood Cemetery, Galena.
