All I've been able to find is that it was persons in the United States, with no mention of it being US citizens or people here legally. I'm still searching though.
I have no idea who was spied on, but the Executive Order doesn't seem to make any such distinctions. Moreover, if they took the time to verify immigration status, why couldn't the Administration's people have gone to the FISA court to get a proper warrant? The FISA court almost never turns down national security requests and it is extremely speedy to boot.
By US persons you mean citizens or aliens here legally? What is known about who was spied on? I can't find any hard info on that.
See 50 USC 1801(i), which defines "United States Person". Under that section of US Code, even a corporation can be a United States Person.
50 USC 1802(i): “United States person” means a citizen of the United States, an alien lawfully admitted for permanent residence (as defined in section 1101 (a)(20) of title 8), an unincorporated association a substantial number of members of which are citizens of the United States or aliens lawfully admitted for permanent residence, or a corporation which is incorporated in the United States, but does not include a corporation or an association which is a foreign power, as defined in subsection (a)(1), (2), or (3) of this section.