Two species of Hepatozoon, i.e., H. sauritus and H. horridus n. sp., were present in 1 of 8 timber rattlesnakes, Crotalus horridus. The narrow gamonts of H. sauritus are 15.0–19.0 × 3.5–5.0 μm, with LW 58–86 μm² and L/W 3.2–4.7, with a narrow, rounded anterior end. The spherical to slightly ovoid oocysts produce ovoid to elongate sporocysts, 21–43 × 12–24 μm, L/W 1.20–2.7, containing on average 22.1 (10–34) sporozoites. This is the first report of a natural cross-familial transfer of a Hepatozoon species. Gamonts of H. horridus n. sp. are 13.0–17.0 × 4.0–6.0 μm, with LW 63–102 μm² and L/W 2.6–4.0, and have broadly rounded ends. The gamont cytoplasm is vacuolated. The spherical to ovoid oocysts form spherical to elongate sporocysts 14–45 × 11–25 μm, L/W 1.0–2.3, producing an average of 13.0 (8–21) sporozoites. The salivary gland in 1 of 5 mosquitoes dissected contained 1 mature oocyst.