Lester Sebastion Willson (June 16, 1839 – January 26, 1919) was a U.S. Civil War officer in the Union Army, Assistant Quartermaster General of New York, and a Montana merchant and politician in Bozeman, Montana. He was married at Albany, New York, on March 2, 1869, to Miss Emma D. Weeks, a native of Vermont. He died in Bozeman, Montana, on January 26, 1919.

Lester Willson was born in Canton, New York, on June 16, 1839, the son of Ambrose and Julia Willson. He was one of seven children and had at least two brothers, Davis and George. His brother Davis would play a prominent role in Lester's later career as a businessman in Montana. He attended public schools in Canton and graduated from a prominent Academy before working as a clerk for two years and then volunteering for the Union Army in 1861.

Willson enlisted in Company A, Sixtieth New York Volunteers, August, 1861, was enrolled second sergeant September 9, 1861, a lieutenant October 3, 1862, first lieutenant and adjutant November 17, 1862. He was offered a captaincy on the same day the adjutant's commission was received, but declined. He was made captain August 2, 1864, lieutenant-colonel October 1, 1864, and colonel May 17, 1865. Willson left the regiment July 17, 1865, as a colonel. On March 12, 1867, he was brevetted brigadier-general of volunteers "for gallant and meritorious services under General Sherman, resulting in the fall of Atlanta, Georgia."

During the winter of 1861-62, Willson participated in guarding the Baltimore and Ohio Railroad and campaigns in Virginia under generals Nathaniel Banks and John Pope. He fought at the Battle of Antietam, September 17, 1862. On May 5, 1863, he was severely wounded at the Battle of Chancellorsville Virginia. He did not return to duty until September 1863 under General Joseph Hooker when the XI and XII Corps of the Army of the Potomac moved westward to reinforce the Army of the Cumberland around Chattanooga, Tennessee. There Willson participated in the battles of Wauhatchie, Lookout Mountain, Missionary Ridge, Peavine Creek, and Ringgold Gap.

In 1864-65 he campaigned under General William Sherman and participated in the Chattanooga campaign, the Atlanta campaign, the Savannah Campaign and the Carolinas campaign.

As an aide, assistant inspector-general, and assistant adjutant-general, Willson was present at significant events during these campaigns. In Atlanta, his regiment, the 60th New York Volunteers share the honor of unfurling the union flag on top of the city hall with the 111th Pennsylvania Infantry. As assistant adjutant-general under the command of General John W. Geary he received the surrender of Savannah at the hands of its mayor R. D. Arnold, and was the first officer to enter the city at the head of his own regiment. The regiment entered the city unopposed and met the mayor and a delegation of the City Council instead of troops. Once Willson received the surrender his regiment quickly began providing protection to the citizens of Savannah from the mobs that had begun breaking into houses and plundering.

Throughout the war Willson enjoyed the confidence of his superiors and on more than one occasion he was entrusted with intricate and dangerous duties by General Sherman. Major General George S. Greene credited him with being a most faithful and intelligent officer, and of his regiment (60th New York Volunteers) Greene has said, "It was one of the best in the service."

At the close of the war Willson held the rank of lieutenant colonel. His successful service and close association with many senior officers caused him to be appointed assistant quartermaster-general of the New York State Militia with the rank of colonel. For two years he was responsible for post-war dealings with the railroad companies regarding the transportation of troops, supplies, etc., the reconciliation of balances between the state and the general government, and the disposition of accumulated supplies belonging to the state.