300m Americans: does it include the 12m illegals?

[jimrtex]

Recently it was said that the USA passed the 300m mark in population. I'm just curious if this meant 300m  citizens, or if it just meant 300m people within the boarders of the USA, including the 12m or so illegal immigrants this country has.

They are intended to be, since the census counts residents.

But the estimates are based on the 2000 Census.  Illegal immigrants may avoid participating in the Census.  They likely move more frequently, so that they were no longer around when followup was done.  In cases where some members of the household are legal and others not, there might be underreporting.  So if a legal resident family has an illegal cousin living with them, he might not show up on the census form.  Even if they weren't illegal, factors such as language and income would tend to have greater underreporting.

Estimates include adjustments to the base for births and deaths, and international migration.  Illegal immigrants might not be counted.

Some states base their population estimates on housing counts and models of persons per household, and tend to be more accurate than the Census Bureau.

The Census Bureau estimate for 2000 which was based on the 1990 Census was about 7 million less than actual population count for 2000.

[jimrtex]

But the estimates are based on the 2000 Census.  Illegal immigrants may avoid participating in the Census.  They likely move more frequently, so that they were no longer around when followup was done.  In cases where some members of the household are legal and others not, there might be underreporting.  So if a legal resident family has an illegal cousin living with them, he might not show up on the census form. 

Non-participation is risky, and participation is not, so I doubt the effect is large. The 2000 census (unlike the 1990 one) was widely applauded as having done a good job of counting everybody, which explains this:

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What is the risk of not participating?  You get something in the mail, you throw it in the trash.  By the time the Census Bureau follows up in person, you've moved.

The state agency population estimates in Nevada and Arizona are diverging from the Census Bureau estimates for those states.  Why?