Are airguns legal everywhere in the US?

Federally, airguns are not firearms because they do not use an explosive (18 USC 921).

15 USC 5001 prevents states from banning the sale of traditional BB and pellet guns to adults. However, several jurisdictions add their own rules: New Jersey (N.J.S. 2C:39-1(f)) and Rhode Island (R.I. Gen. Laws 11-47-2(7)) classify all airguns as firearms; Illinois treats airguns as firearms when they exceed both .18 caliber and 700 fps; Michigan exempts smoothbore .177-caliber-only BB guns; New York City requires a license under NYC Admin Code 10-131(b). Always check your state and city before buying.