The 121st New York Infantry Regiment, commonly known as the "Onesers" or "Upton's Regulars", was a volunteer regiment recruited during the American Civil War from Otsego County and Herkimer County, New York. The Hon. Richard Franchot was appointed colonel of the regiment and authorized to establish his headquarters at Richfield Springs, Otsego County. He proceeded without delay to organize the regiment, and on August 23, 1862, the regiment was mustered into the service of the Union Army. The command at that time consisted of 39 officers and 946 enlisted men. The 121st Regiment proceeded to Washington, arriving there on the morning of September 3, and was assigned provisionally to a brigade under Colonel Gibson with headquarters at Fort Lincoln.

Emory Upton was a United States Army general and military strategist, prominent for his role in leading infantry to attack entrenched positions successfully at the Battle of Spotsylvania Court House during the American Civil War, but he also excelled at artillery and cavalry assignments. His work, The Military Policy of the United States, which analyzed American military policies and practices and presented the first systematic examination of the nation's military history, had a tremendous effect on the U.S. Army when it was published posthumously in 1904.