Cognomen Declain (Declain 
) , around the globe, is an extremely rare last name. The cognomen Declain is habitual in Latin America and the Caribbean, particularly Mexico, where it is an extremely rare surname. Much more prevalently, Declain is the forename as well as the last name.
| VARIANT | COUNTRY |
|---|---|
| Declain | United Kingdom, Mexico, United States, Brazil, Democratic Republic of the Congo |