Go to the county clerk or tax district and they should either have maps or be able to tell you. To trespass there does NOT have to be a fence (sorry Braineack). Here is Cornell Law Library's definition, notice no mention of fencing: "Trespass is defined by the act of knowingly entering another person’s property without permission. Such action is held to infringe upon a property owner’s legal right to enjoy the benefits of ownership." Full definition here: Trespass As an amateur wildlife photographer and avid birder it is at time tempting but . . . I live in Texas, so crossing that boundary (fence or "line in the dirt") could be hazardous. Be safe and smart.