When does autumn begin in North America?

The exact date that autumn begins can vary slightly from year to year, but it generally begins around September 22 or 23 in North America. This date marks the autumnal equinox, which is when the day and night are of equal length. After the autumnal equinox, the days start getting shorter, and the nights start getting longer. The weather also starts to change, becoming cooler and wetter. Leaves on deciduous trees start to change color and fall off. This is a sign that autumn has begun.