Dayton is a city in Webster County, Iowa, United States. The population was 772 at the time of the 2020 census. A post office called Dayton h…Dayton is a city in Webster County, Iowa, United States. The population was 772 at the time of the 2020 census. A post office called Dayton has been in operation since 1877. The city was named after Dayton, Ohio.