Triangle Park is a former American football stadium located in Dayton, Ohio. The stadium was opened in 1916 as a company baseball field for employees of Dayton Engineering Laboratories, a Dayton firm established in 1909. Soon after the park's establishment it was expanded by an additional four acres of land adjacent to the park abutting the Stillwat…Triangle Park is a former American football stadium located in Dayton, Ohio. The stadium was opened in 1916 as a company baseball field for employees of Dayton Engineering Laboratories, a Dayton firm established in 1909. Soon after the park's establishment it was expanded by an additional four acres of land adjacent to the park abutting the Stillwater River.