Legislation to establish a Sand Creek Massacre National Historic Site began in 1998 with passage of Public Law 105-243, sponsored by Colorado Senator Ben Nighthorse Campbell. This bill is known as the Sand Creek Massacre National Historic Site Study Act.

A Site Location Study mandated that the National Park Service determine the location and extent of the Sand Creek Massacre. In 1999, a Sand Creek Massacre Project Team, and other researchers, began to piece together answers. Oral history, remote imagery, historical documentation, archeology, aerial photography and other methods were used. The Sand Creek Massacre Project Team, along with other research, was able to identify several areas along Sand Creek where the activities of November 29 and 30, 1864 likely took place.

After completion of the Site Location Study, the Sand Creek Massacre National Historic Site was officially authorized on November 7, 2000.

As a running engagement, the Sand Creek Massacre continued up Sand Creek and across its valley onto the surrounding plains and bluffs - this area, about 7,500 acres, stretches for a number of miles. Though debate continues regarding the specific location of internal features, most researchers agree that the core area of the site (listed with The National Register of Historic Places), contains the location of the Indian village; the point(s) from which the Colorado regiments first spotted the encampment; the location of Indian pony herds; the general path of battalion advancements, skirmishing, and other collateral action; the military bivouac area of November 29-30; spots in the stream and along its banks where the Cheyenne dug pits from which to hide and fight; and the points from which battery salvoes were launched into the camp and later into the pits.

On August 2, 2005 the Sand Creek Massacre National Historic Site moved a step closer to its establishment with the passage of P.L. 109-45, the Sand Creek Massacre National Historic Site Trust Act.

In 2007, Sand Creek Massacre National Historic Site was established as a National Park Service unit.