Hsinyi is located in the south-eastern portion of Nantou County flanked in the east by Hualien County, by Shuili and Luku to the west, by Chiayi to the south and Jenai to the north.
信義鄉位於南投縣東南端，是縣內二個山地鄉之一，東接花蓮，南連嘉義，西鄰水里、鹿谷、北界仁愛，面積約一千四百平方公里，佔南投縣的三分之一，比彰化縣還大。