After finally recovering enough for field command, Kimball was assigned to duty in the Western Theater, reporting in June 1863 to Corinth, Mississippi, where he assumed command of a division in the XVI Corps. His was one of three divisions in that corps that were ordered to Mississippi in to join the Siege of Vicksburg, although they arrived too late to participate in much of the actual fighting. In September, the greater part of Kimball's division was ordered to Arkansas, where it became incorporated in the VII Corps. He commanded the rear echelon in the Camden Expedition.