De Lannoy or Delannoy is a surname, and may refer to;
- Noble Belgian House of Lannoy
- Others
- Albert Delannoy, long jumper
- Colinet de Lannoy, composer
- Eustachius De Lannoy, naval commander
- Henri Delannoy (1833–1915), French military officer and amateur mathematician
- Jean Delannoy, actor and film director
- Louis De Lannoy, cyclist
- Luc Delannoy [es], writer and philosopher
- Marcel Delannoy (1898–1962), French composer
- Claire Delannoy, French writer
- Robert Delannoy, World War I flying ace
- Sandra Delannoy, French politician