Surname Thellefsen (Thellefsen 
) , all over the world, is a very rare cognomen. The family name Thellefsen is habitual in Denmark, where it is quite a rare surname, Canada, where it is an extremely rare surname, and the United States.
| VARIANT | COUNTRY |
|---|---|
| Thellefsen | Canada, Denmark, United States |
| leo thellefsen Danish painter (b. 1909) |
|