The company's sales fell to 169,656 vehicles last month, in the United States, from 203,100 vehicles in September a year earlier, and were the lowest since January, led by a 16.8% fall in its pickup trucks and SUV sales.
In the third quarter, Toyota's U.S. sales fell 1.2% to 627,194 vehicles.
One big reason Toyota and other automakers are reporting lower sales this month: Because of the timing of Labor Day weekend this year, it was counted in August sales. By this year's calculations, September only had 23 selling days.
Other automakers' results:
Mazda: Total September sales of 18,838 vehicles, a decrease of 11.4%. Year-to-date sales through September are down 11.5%, with a total of 208,167 vehicles sold in the U.S.
Volvo: Volvo sold 9,323 vehicles in the U.S. in September, up 7% from September 2018. It has sold 77,432 vehicles year-to-date, up 4.7% from 2018.
Volkswagen: VW of America reported 26,947 total units sold in September, down 12% from September 2018, but with year-to-date sales up 4.5%.
BMW: BMW brand sold 27,467 vehicles in September, up 6.0% from 2018.