Just because a state doesn't have a law allowing breastfeeding in public, doesn't mean it's illegal. Check that state's indecent exposure law.
Idaho - 18-4116. Indecent exposure. Every person who willfully and lewdly, either:
(1) Exposes his or her genitals, in any public place, or in any place where there is present another person or persons who are offended or annoyed thereby; or,
(2) Procures, counsels, or assists any person so to expose his or her genitals, where there is present another person or persons who are offended or annoyed thereby is guilty of a misdemeanor.West Virginia - §61-8-9. Indecent exposure.
(a) A person is guilty of indecent exposure when such person intentionally exposes his or her sex organs or anus or the sex organs or anus of another person, or intentionally causes such exposure by another or engages in any overt act of sexual gratification, and does so under circumstances in which the person knows that the conduct is likely to cause affront or alarm.
This list provides all the laws for every state and territory. http://www.ncsl.org/issues-research/health/breastfeeding-state-laws.aspx