The first clear evidence for cultivated plants in North America comes from Koster,Illinois dating back to c.5,000 BC. https://commons.wikimedia.org/wiki/File%3ACOLLEGE_STUDENTS_WORK_WITH_ARCHAEOLOGISTS_AT_%22KOSTER_DIG%22_AN_ANCIENT_INDIAN_BURIAL_SITE_-_NARA_-_552495.jpg
Rind fragments of squash were found in Koster, Illinois. Some of the oldest evidence of the use of ground stone for food preparation was also found at this site. Barker, Graeme. “Foraging and Floodplain Weed Cultivation in Eastern North America.” The Agricultural Revolution in Prehistory: Why Did Foragers Become Farmers? Oxford: Oxford UP, 2006. 239. Print.
The Koster site is also known for revealing one of the earliest instances of dog burials/domestication as well as established cemeteries for lovesd ones.