Toxoplasmosis is a zoonosis of reproductive nature that is transmitted to humans mainly by ingestion of undercooked meat or drinking oocyte-contaminated water. The slaughter of small ruminants in clandestine slaughterhouses and the presence of companion animals in these locations may be epidemiologically important for the dissemination of the disease. The objective of the present study was to determine toxoplasmosis prevalence by researching anti-Toxoplasma gondii antibodies in meat sheep herds from farms in Teresina microregion, Piauí, Brazil. A total of 450 blood samples were collected from sheep of both sexes, belonging to 28 herds from the 14 municipalities that comprise the microregion. The samples were analyzed by the enzyme-linked immunosorbent assay (ELISA), and the presence of anti-T. gondii antibodies was observed in 62% (279/450) of the animals in all the municipalities and on at least one farm in each municipality. The high occurrence of positive animals is an indication of reproductive problems in these herds, characterizing a problem for both sheep rearing and public health.