Johnston is a city in Polk County, Iowa, United States. The population was 8,649 at the 2000 census; the United States Census Bureau estimated that 15,691 residents lived there in 2008. It is part of the Des Moines–West Des Moines Metropolitan Statistical Area. Johnston is the location of the headquarters of Pioneer Hi-Bred Seeds, Iowa Public Television, and The Gardeners of America/Men's Garden Clubs of America. The Camp Dodge Military Reservation is also located here.