Those property taxes also are based on what you paid for the property , If they had not been reviewed by the county /city for many years and stayed low because the previous owner paid very little for the land. Of course when some one else comes in and is the new owner in many places that is one of the times they review the taxes and see if they need to be changed . So if property sales values went way up in that area so too would the taxes . Have you looked at comparable property in that area/county to see what it is selling for and looked at what the public records show the taxes are on those properties ? that kind of information might help you alot in any attempt to get those taxes reduced . So do some digging and see what you learn . (also if you were planning just by chance on building a home for your self using all 3 to be your lot see if the taxes will drop by having the parcels combined into one parcel .)