According to the Wyoming State Historical Society, on September 18, 1890, two passenger trains collided near Rock Springs. Only one person was injured. Also on September 18, but a few years later in 1893, Capt. William Kieffer and others climbed the Grand Teton. They claimed later to be the first to make the ascent. On September 19, 1920, a bank president was struck and killed by lightning in Moorcroft. On September 24, 1906, President Theodore Roosevelt designated Devils Tower as the first national monument in the state. Just under three years later, on September 21st, 1909, President Taft designated Shoshone Cavern National Monument as the second national monument created in Wyoming. And on September 24, 1869, celebrity suffragist Anna Dickinson spoke to 250 people in Cheyenne.

According to the Wyoming Almanac, on September 18, 1986, two inches of rain fell in 45 minutes in Wheatland. On September 20, 1983, a temperature of -15 degrees was reported in Big Piney.