Älmsta or Elmsta is a locality situated in Norrtälje Municipality, Stockholm County, Sweden. It had 924 inhabitants in 2005 and 1,097 in 2010. Elmsta is the old Swedish name, which has become more popular again, while Älmsta still is the official name. Älmsta is situated at the northern end of the Väddö Canal, an artificial canal first dug in the 16th century to provide a sheltered passage between the Bagghusfjärden to the south and the Väddöviken to the north.