The Constitution is very clear about counting every "person," not just every "citizen," sooooo...
The use of the word "in" is ambiguous.
Is someone who is traveling from London to Mexico City and miss their connecting flight in Atlanta on April 1, they are literally in Georgia, but are they counted?
What about if they are on a tourist visa for a month? Six months? What if they overstay the visa and get a job?
Is an illegal alien who is incarcerated with a hold so that he can be deported when the sentence is completed be counted? What about someone who is detained in an ICE facility?