If you mean by “plat number” the surface tract, they could give you at least 2 websites to use. An account (tax) that is just minerals will have a prefix for the district, then “9999” meaning minerals or at least not surface, then a (maybe) 8 digit number. A surface tract would have the prefix for district, then a number for the tax map then a number for the parcel number and maybe a suffix number for a parcel that has been subdivided, for the smaller part. I believe that you are going to have to dig a little more to get the full answer. People here can help if you want to learn. Or wait. If your great grandfather (I think this is where the inheritance starts) was paying a tax bill that somehow has been passed down and is still being paid by a cousin, that cousin will be hit by a giant leap in the tax bill in a couple of years.