Hydromedusa maximiliani is a freshwater turtle endemic to the Atlantic Forest of eastern and southeastern Brazil and threatened by extinction. Here, we add 15 new locality records for this species based on photographs of specimens encountered in the field and examination of museum collections. We also used ecological niche modeling tools of 3 different algorithms (GARP, SVM, and Maxent) to suggest potential suitable areas for the occurrence of the species. Models predict 53,679–263,844 km2 of suitable habitat for H. maximiliani, with 8396–31,758 km2 inside protected areas. Besides being useful in a reassessment of the species' conservation status, our results contribute to the knowledge of distribution patterns of H. maximiliani and highlight potential areas to drive future field surveys.