There about 45 million foreign-born persons in the U.S. 13.4 million are green card holders: 9.4 million (70%) here due to family; 1.6 million (12%) with employment-based visas; 1.6 million (12%) refugees; and somewhat less than million for other reasons.
An additional 11 million are here illegally. The remainder, 21 million, are naturalized citizens. About three quarters of green card holders eventually naturalize. The number eligible to naturalize has remained steady at about 9 million.