Johan Arthur Castrén (10 June 1866 – 29 June 1946) was a Finnish politician, born in Turtola. He was a member of the Senate of Finland and the first director of internal affairs[1] from 27 November 1917 to 27 November 1918, before the Ministry of Interior was created. He served as Mayor of Helsinki from 1931 to 1936. He died in Jakobstad.