A new species of Eimeria Schneider, 1875 (Apicomplexa: Eimeriidae) collected from an ornate box turtle, Terrapene ornata (Agassiz) from Arkansas, USA, is described. Oöcysts of Eimeria doddi n. sp. are ovoidal to ellipsoidal with a smooth, light to darker brown, bi-layered wall, measure 21.1 × 14.0 µm, and have a length/width (L/W) ratio of 1.5; both micropyle and oöcyst residuum are absent, but a polar granule is present. Sporocysts are ellipsoidal, 9.9 × 6.1 µm, L/W 1.6; the Stieda body is present, but the sub-Stieda and para-Stieda bodies are absent and the sporocyst residuum is composed of small granules in a cluster. Sporozoites have a spheroidal anterior refractile body, a subspheroidal posterior refractile body, and one centrally-located nucleus. This is the third description of an eimerian from the turtle genus Terrapene Merrem and the second from T. ornata. In addition, we report Eimeria ornata McAllister & Upton, 1989 from T. ornata from Texas.