The New Plymouth Sub-District Of The Wanganui Police District was constituted in 1898. Originally, New Plymouth was the head of the district, but in 1898 Wanganui became the principal office. The sub-district includes Mokau, Waitara, Inglewood and Rahotu. The staff includes a sergeant-in-charge, five constables, and a detective, and the police office is in Silver Street, New Plymouth.

Mr. Walter H. Hadrell, Sergeant-in-charge at New Plymouth, was born in Devonshire, England, in 1850. He came out to Canterbury in 1866, and joined the police under the Provincial Government, at Christ-church in 1872. He was promoted to a sergeantship in 1898.