The most reliable solution is to contact a surveyor who can determine the corners of your property, then tie off string lines to mark the property lines. The Property Viewer web app shows property lines which are fairly accurate, but are representations based on data that may not be 100% accurate.
If your property is platted, the Register of Deeds can give you the dimensions of your lot from the recorded plat of your subdivision or you may request a copy of your recorded plat (fees apply). The only way to know the exact property lines of any platted or unplatted piece of property is to have a formal survey performed.