Cognomen Mathias-Day (Mathias-Day 
) , around the world, is an extremely rare family name. The last name Mathias-Day is characteristic of Northern America, particularly the United States, where it is an extremely rare surname. Parts of the name also exists independently as a first name Mathias, and a last name Day.
| VARIANT | COUNTRY |
|---|---|
| Mathias-Day | United States |