Generally speaking, ignorance of the law is no defense. Everybody knows it's illegal to peddle drugs, to drive while intoxicated, or to steal, and any plea of ignorance of the law against these infractions would be ridiculous. In cases of less serious infractions and misdemeanors, it may be less obvious what the law is. You're still responsible for obeying the law, but you may be able to convince a court that it wasn't your intention to break the law. There are many laws -- federal, state, and local -- and it's unlikely that you're aware of all of them. Many local governments have ordinances, which are specific to their areas of jurisdiction, and there's a distinct possibility that you may be unaware of at least some of these regulations. Assuming that you're admitting your guilt, you may be able to make a case for leniency based on your prior unawareness of the crime and your resolve not to repeat the offense. Ignorance of the law remains an invalid defense, but in simple infractions or misdemeanors, it may encourage a court to be lenient.
