Illegal: (adjective) against the law
This word can NEVER be used to describe a human being. Period. It can’t be a noun either.
An action can be illegal:
- It is illegal to steal.
- His involvement in the crime was illegal.
A thing can be illegal:
- The website was taken down for illegal content.
- The modifications to the car made it illegal on the roads.
But a human’s existence or presence in a country is never illegal.