Last name O Neil (O Neil 
) , in all the world, is a rare cognomen. The family name O Neil is habitual in Ireland, where it is quite a rare surname, Uruguay, where it is a rare surname, and the United States. Measured by absolute frequency, the name is most common in the United States, Ireland, and the United Kingdom. Very seldom, O Neil is the forename as well as the last name.
| VARIANT | COUNTRY |
|---|---|
| O Neil | Canada, Spain, Ireland, United Kingdom, United States |