The first American Indian Day was celebrated in May 1916 in New York. In 1990, then President George H. W. Bush signed a joint congressional
resolution designating National American Indian Heritage Month. Similar proclamations have been issued every year since 1994.
In 1994 the state General Assembly established the "fourth Monday in September of each year" to be especially observed in Tennessee as "American Indian Day" (TCA 15-2-106), "to recognize the contributions of American Indians with suitable ceremony and fellowship designed to promote greater understanding and brotherhood between American Indians and the non-Indian people of the state of Tennessee".
Source: tn.gov
In 2020 American Indian Day in Tennessee in USA falls on September 28.