Summer comes to an end this Wednesday, September 22nd, at 10:09 pm CDT, during the Autumnal Equinox.
The word "equinox" comes from a Latin term meaning "equal night", and refers to the time when the sun crosses the equator. While it is generally believed that everyone has 12 hours of sunlight on this particular day, and the sun rises directly in the east and sets directly in the west, the exact date that will occur depends on the latitude of the location. For example, in Springfield, sunrise on the 22nd is at 6:46 am and sunset is at 6:56 pm, for a total of 12 hours 10 minutes of sunlight. Additionally, the sunrise is technically 1.02 degrees north of due east (see image below) at sunrise and 0.77 degrees north of due west at sunset, although this is imperceptible for all practical purposes.
September 26th is closest to having exactly 12 hours of sunlight in Springfield (sunrise 6:50 am, sunset 6:49 pm).