Answer: true
Explanation: According to the TravelWinsconsin site, there is an stimate of 15,000 to 20,000 effigy mounds created (raised pile of earth built in the shape of a stylized animal, symbol, human, or other figure and generally containing one or more human burials) by the Native Americans in Winsonsin, and around 4,000 of these remaing to the day.
So the statement is true.