Ticks are common on horses, but there is a dearth of contemporary data on infestation prevalence, predominant species, and tick-borne disease agents important in this host. To determine the species of ticks most common on horses and the prevalence of equine exposure to and infection with tick-borne disease agents, ticks and blood samples were collected from 73 horses during May, June, and July of 2010. Adult ticks were identified to species, and antibodies to Ehrlichia spp., Anaplasma spp., and Borrelia burgdorferi were identified using indirect fluorescence antibody assay, a commercial point-of-care enzyme-linked immunosorbent assay, or both. In total, 1,721 ticks were recovered at the majority (85%) of equid examinations. Amblyomma americanum (L.) was the most common tick collected (1,598 out of 1,721; 92.9%) followed by Dermacentor variabilis (Say, 1821) (85 out of 1,721; 4.9%) and Amblyomma maculatum Koch, 1844 (36 out of 1,721; 2.1%); single specimens of Ixodes scapularis Say, 1821 and Dermacentor albipictus (Packard, 1869) were also identified. Antibodies reactive to Ehrlichia spp. were found in 18 out of 73 (24.7%) of horses tested, and were more commonly identified in horses with moderate or high tick infestations than those with low tick infestations (P < 0.001). These data support A. americanum as the most common tick species infesting horses in central Oklahoma from May through July and suggest horses are also commonly exposed to an Ehrlichia sp.