Is jailbreaking legal in the united state?

Yes, "the courts have long recognized that copying software while reverse engineering is a fair use when done for purposes of fostering interoperability with independently created software."

Apple-says-jailbreaking-illegal">http://www.eff.org/deeplinks/2009/02/Apple-says-jailbreaking-illegal

Jailbreaking does not load a torrent app or allow installation of pirated apps. Those services are a separate and illegal venture that are commonly linked with jailbreaking, thus giving jailbreak a bad name.