Strict liability crimes are those in which the defendant is held liable for a criminal offense he committed, even if mens rea is absent. Though the defendant did not intend any harm by his actions and was completely unaware that he was committing an illegal act, the doctrine of strict liability holds him liable for the criminal offenses committed.
Because of the respect for due process in the United States, the vast majority of strict liability crimes are less serious offenses. Most cases of strict liaiblity are minor infractions and misdemeanors, not nearly as serious as felonies, but still warranting heavy fines and up to a year in jail. Examples of minor offenses for which violators are held strictly liable are parking violations, speeding unknowingly, selling alcohol to minors and, in some jurisdictions, employing people under the age of fourteen.
A few strict liability crimes do qualify as felonies in some states. Statutory rape is one such crime. Classified in widely varying ways from state to state, sexual congress between a minor and a legal adult can carry very heavy penalties, sometimes even decades in prison, even if the activity was completely consensual and the adult had every reason to believe that he had been with another legal adult (appearance, verbal inquiry, even checking a fake ID).