Post Falls is a city in Kootenai County, Idaho, United States. It is the gateway city to North Idaho on I-90 just west of Coeur d'Alene and e…Post Falls is a city in Kootenai County, Idaho, United States. It is the gateway city to North Idaho on I-90 just west of Coeur d'Alene and east of Spokane, Washington. The population was 38,485 at the 2020 census, making it Idaho's ninth-largest city and the second largest city in North Idaho behind Coeur d’Alene.