Born in Yazoo County, Mississippi, to Charles L. and Maria I. Buck. His father was "one of the most eminent jurists and advocates of his state", and one of the few prominent Mississippians to publicly oppose secession during the American Civil War, and his mother was a well-regarded author. Buck's father died in Vicksburg, Mississippi in 1862, and the family remained in that city during the 47 day siege that ran from May 18, 1863 to July 4, 1863. During this time, the family had to live in the cellar of the house to escape the risk of Union bombardment. After the war ended, the family moved to Bayou Teche area in St. Mary Parish, Louisiana, and then in 1869 to join relatives living outside Sedalia, Missouri.