Where can I find official maps of property boundaries?

Answer 1

at your county clerks office.

Answer 2

The county keeps them in the United States. In Texas plats of individual properties can be found online at many appraisal districts. To get a copy of the boundries in an area may require a visit to the office where a book has the plat markings by subdivision, block or other area.
One problem, having gotten the paper, is locating it exactly on the ground. My plat says the corner is a certain specific distance from a nearby street which is shown on the larger map, but there are no curbs or other markings at the street to locate where to measure from. Half the houses behave as if they own property a foot or more onto other people's property.