What is the average IQ for someone in the US?

"someone" is a singular form.

"someone in America"[sic] is still singular.

Depending on who this "someone" is, the answer you seek is his/her IQ divided by 1, therefore providing the number of his/her IQ.

If this "someone" is you, the average you ask for is probably within the range from 70 to 80.