Millville is a city in Cache County, Utah, United States. The population was 2,222 at the 2020 census, with an estimated population of 2,300 in 2…Millville is a city in Cache County, Utah, United States. The population was 2,222 at the 2020 census, with an estimated population of 2,300 in 2022. It is included in the Logan, Utah-Idaho Metropolitan Statistical Area.