The Rape, Abuse, and Incest National Network has some helpful links and information on their site: http://www.rainn.org
One page is dedicated to definitions of rape and sexual assault: http://www.rainn.org/statistics/definitions.html
It's also advised: "To determine the statute in your state, contact your local prosecutor, district attorney or state attorney general's office. You can also read more about the laws in your state."
RAINN's Page on State Laws on Statutes of Limitations: http://www.rainn.org/what-should-i-do/state-laws.html
Cornell University's Legal Information Institutehas a good list of links to state criminal/ penal codes: http://www.law.cornell.edu/topics/state_statutes2.html#criminal_code