THAT IS WHAT THE CONSTITUTION SAYS TO DO! The "Census clause" or sometimes called the "Enumeration clause" is found in Article I, 1, § 2, cl. 3 of Constitution. After taking into account the removal and additions that have occurred with later amendments, that clause reads as follows: "Representatives . . . shall be apportioned among the several States . . . according to their respective Numbers . . . . The actual Enumeration shall be made within three Years after the first Meeting of the Congress of the United States, and within every subsequent Term of ten Years, in such Manner as they shall by Law direct." Further, Section 2 of the Fourteenth Amendment states that "Representatives shall be apportioned among the several States according to their respective numbers, counting the whole number of persons in each State, excluding Indians not taxed."
The Constitution uses the word "numbers" and "persons" -- not "citizens," or "legal residents," or "those lawfully present". Everyone must be counted!