Arlington Heights is a municipality in Cook County in the U.S. state of Illinois. A suburb of Chicago, it lies about northwest of the city's downtown. Per the 2020 Census, the population was 77,676. Per the 2010 Census, it is the most populous community in the United States that is incorporated as a "village", and is the 13th most populous municipality in Illinois, although it is not far ahead of its nearby Illinois neighboring villages of Schaumburg and adjacent Palatine. Arlington Heights is known for the former Arlington Park Race Track, home of the Arlington Million, a Breeders' Cup qualifying event; it also hosted the Breeders' Cup World Thoroughbred Championships in 2002. The village is also home to the Arlington Heights Memorial Library, which has one of the largest collections of books in the state. History Arlington Heights lies mostly in the western part of Wheeling Township, with territory in adjacent Elk Grove and Palatine townships, in an area originally notable for the absence of groves and trees. Pre-Settlement History The land that is now the Village of Arlington Heights was controlled by the Miami Confederacy (which contained the Illini and Kickapoo tribes) starting in the early 1680s. The Confederacy was driven from the area by the Iroquois and Fox in the early 1700s. The French-allied Potawatomi began to raid and take possession of Northern Illinois in the 1700s. In the late 1700s and early 1800s, the Potawatomi expanded southwards from their territory in Green Bay and westward from their holdings near Detroit, until they controlled in an L-shaped swath of territory from Green Bay to the Illinois River, and from the Mississippi River to the Maumee River. Throughout the 1830s, the Potawatomi maintained a camp in modern-day Arlington Heights that was used for six weeks out of the year as the Potawatomi migrated from their summer encampments to their winter encampments. In 1833, the Potawatomi signed the 1833 Treaty of Chicago with the United States Government. As a result of the Treaty, the United States was granted control of all land west of Lake Michigan and east of Lake Winnebago in exchange for a tract of land west of the Mississippi. The land that is now Arlington Heights was ceded to the U.S. in this treaty, which sparked mass white immigration to the Northern Illinois area. The U.S. Government purchased the land for about 15 cents per acre, and