Two maps in McPheeter’s book, pp. 74 & 122, only show it as immediately adjacent East of Spring Hill

Camp Sumter was the name given to the army’s new winter quarters in the vicinity of Spring Hill, Hempstead County, Arkansas p. 355, Note 4

Our headquarters is at Spring Hill near Red River and mid-way between Lewisville and Washington. The officers occupy a large female seminary building admirably adapted for accommodating the staff officers with comfortable rooms for officers and sleeping apartments. pp. 111/12