Carlos Botelho State Park (PECB) is a protected area of an important Atlantic Rainforest remnant in São Paulo State, Brazil, affected by the growth of surrounding neighborhoods and the increase of domestic animals freely roaming inside and outside the park. Overpopulation of free-ranging domestic dogs is an issue faced by many protected areas, resulting in intimate contact with wild mammals. This situation increases the flow of infectious diseases between them, posing a threat to the wild populations. Toxoplasma gondii is a parasite that infects warm-blooded animals and its definitive hosts are wild and domestic felids. Once one infected domestic dog enters the park it can infect a wild predator mammal and contribute to the disease dynamic. In order to implement interventions regarding the local domestic dogs we evaluated habitants of the surroundings of PECB, and antibody anti-T. gondii was detected in 28% (100/350) and 25% (101/396) of the animals from 2015 and 2016, respectively. Among the 252 dogs sampled on both years, 33 were positive. The dogs entering the park probably act as predators as well and the high T. gondii seroprevalence shows the spread of this agent at that preserved area. Those results will foster the buildup of a health management model for the surroundings of the park. Implementation of permanent public policies including joint actions to minimize the access of feral domestic dogs into the park and their contact with wild carnivores, such as neutering and health education campaigns, could enhance the survival of local wild species.