Cahokia Mounds was first protected by the state of Illinois in 1923 when its legislature authorized purchase of a state park.
Later designation as a state historic site offered additional protection, but the site came under significant threat from the federal highway building program in the 1950s.
The highway program reduced the site's integrity; however, it increased funding for emergency archeological investigations.
These investigations became intensive, and today continue, and have led to the present understanding of the significance of the site.
The site was designated a National Historic Landmark on July 19, 1964, and listed on the National Register of Historic Places on October 15, 1966.

In 1982, UNESCO (the United Nations Educational, Scientific and Cultural Organization) designated the site a World Heritage Site.
This is the only such self-contained site in Illinois and among only 24 World Heritage Sites in the United States.
State Senator Evelyn M. Bowles wrote about the Cahokia Mounds site:
Through the years my friends and I made occasional Sunday afternoon trips to the Mounds.
When I became the State Senator, it afforded me the opportunity to secure funds for the acquisition of additional acreage in which there are smaller Mounds.
Many of these have contained additional artifacts."
The designation has helped protect the property and attract funds to conduct research on this significant civilization.
Cahokia Mounds was first protected by the state of Illinois in 1923 when its legislature authorized purchase of a state park. Later designation as a state historic site offered additional protection, but the site came under significant threat from the federal highway building program in the 1950s. The highway program reduced the site's integrity; however, it increased funding for emergency archeological investigations. These investigations became intensive, and today continue, and have led to the present understanding of the significance of the site. The site was designated a National Historic Landmark on July 19, 1964, and listed on the National Register of Historic Places on October 15, 1966.
In 1982, UNESCO (the United Nations Educational, Scientific and Cultural Organization) designated the site a World Heritage Site. This is the only such self-contained site in Illinois and among only 24 World Heritage Sites in the United States. State Senator Evelyn M. Bowles wrote about the Cahokia Mounds site:
Through the years my friends and I made occasional Sunday afternoon trips to the Mounds. When I became the State Senator, it afforded me the opportunity to secure funds for the acquisition of additional acreage in which there are smaller Mounds. Many of these have contained additional artifacts." The designation has helped protect the property and attract funds to conduct research on this significant civilization.
Cahokia