Do you mean parcel dimension, not house? Is so, definitely get a survey. Don’t trust county plat maps or other sources. They are good, but a surveyor will measure exactly and be a lot more appropriate for legal actions/discussions.
If you’re really talking about house boundaries, dpending on the year built, the county building department might have the original plans in their archives, but I wouldn’t bet on it. If it’s a production builder home from recent years (and you can’t get it from them), there are some services that collect floor plans from the builders when the models are open and sell them.
