First Day Autumn 2024.  — usually, when we talk about the first day of autumn we are referring to the astronomical autumn which is defined by the earth's axis and orbit around the sun. The first day of fall is sunday, september 22, 2024—the same day as the autumn equinox—in the northern hemisphere.

The first day of fall is sunday, september 22, 2024—the same day as the autumn equinox—in the northern hemisphere.  — in 2024, the fall equinox will be sunday, september 22, according to almanac.com.