"Trespassing" is a legal term that can refer to a wide variety of offenses against a person or against property. Technically, a person violates the law against trespassing by knowingly going onto someone else's land without consent. "Knowledge" may be inferred when the owner (or the owner's representative) tells the trespasser not to go on the land when the land is fenced in a manner that suggests that intruders should stay out or there is a "no trespassing" sign in an obvious place.
A trespasser will probably not be prosecuted if the land was open to the public when the trespasser originally entered the land and the trespasser's conduct did not substantially interfere with the owner's use of the property and the trespasser left on request. Violating this law is a Class C misdemeanor.
The more serious crime of "aggravated criminal trespass" combines trespassing with conduct that would cause fear for someone's safety. This is a Class B misdemeanor. If the "aggravated criminal trespass" is committed in a house or a hospital or a school, it is a Class A misdemeanor. One word of caution: sometimes posting a "no trespassing" sign can backfire. Because the "adverse possession" rules are so complicated, posting a "no trespassing" sign can actually help a trespasser support a claim to the owner's property.
One common form of trespassing is when a neighbor's driveway or fence encroaches onto someone else's land. Sometimes the owner will not want to make an issue of the encroachment--either because it seems to be a minor problem or because the neighbor is a friend. To avoid problems later, however, the owner should give the "trespasser" written permission to keep the encroachment for as long as the owner...