Born to an affluent family in 1836, Hylan B. Lyon claimed ancestors among Irish rebels, patriots of the American Revolution, and slaveowners in his native Kentucky. Biographer Dan Lee chronicles Lyon's military career, which began with service in the Third US Artillery after his graduation from West Point in 1856. Lyon first saw action in the Third Seminole War. Later stationed at Fort Yuma in California, he went on to fight in the Coeur d'Alene War. Witnessing the execution of Yakima chief Qualchan during this last conflict nearly made Lyon leave the army. Yet the young lieutenant persevered. After serving with troops building the Mullan Road between Washington and Montana, Lyon returned to Kentucky just as Lincoln won the 1860 presidential election. Though his home state never seceded from the Union, Lyon cast his lot with the Confederacy. He served with the Third Kentucky Infantry Regiment (CSA), led the Eighth Kentucky Infantry, and later commanded the Kentucky Brigade under Gen. Nathan Bedford Forrest. Lyon saw action in Kentucky, Tennessee, Alabama, and Mississippi, spending several months as a prisoner of war and winning special commendation for his performances at the Battles of Coffeeville and Brice's Crossroads. He ultimately earned the rank of brigadier general.

After the Civil War, Lyon sought refuge with other ex-Confederates in Mexico, working as a railroad surveyor. He requested and received a presidential pardon and returned to Kentucky by mid-1866. Lyon remained there until his death in 1907, devoting himself to farming and prison reform, as well as serving in the state house of representatives. He was the mayor of Eddyville, Kentucky, when he died in 1907.