Purdin is a city in northwest Linn County, Missouri, United States. The population was 141 at the 2020 census. Purdin was platted in 1873. …Purdin is a city in northwest Linn County, Missouri, United States. The population was 141 at the 2020 census. Purdin was platted in 1873. The community was named for its founder, Allen W. Purdin. A post office called Purdin has been in operation since 1877.