Although early reports locate Aché-like groups throughout eastern Paraguay and the adjacent areas of Brazil, by the 20th century the Aché lived in four dialectally distinct groups that inhabited the Paraná River watershed in the modern day Paraguayan states of Caazapa, Guairá, Alto Paraná, Caaguazu, and Canindeyu.
Eastern Paraguay is characterized by gently rolling hills covered with subtropical, semideciduous forest, and low flat valleys filled with tall grasses.