Which site in Chicago's history existed before the city's incorporation?

Fort Dearborn is the correct answer because it was established in 1803, well before Chicago was officially incorporated as a city in 1837. The fort served as a military outpost and played a significant role in the early settlement and development of the area. Its existence influenced both the strategic and residential growth of what would become Chicago.

In contrast, Wrigley Field, Millennium Park, and Navy Pier were all developed much later. Wrigley Field was built in 1914, Millennium Park was opened in 2004, and Navy Pier was completed in 1916. These sites reflect the later urban and recreational developments in Chicago, whereas Fort Dearborn is a landmark that precedes the city's formal establishment.