Land- Land kits you buy from the EP store are yours. Also known as the dreaded ancestral land. Land for town purposes can be incorporated into the town and you lose ownership of said land.
Buildings- Building you buy and put on ancestral land are yours. Buildings you buy and put on town land become part of the town...(I think).
Everything else you buy I figure apply the same logic.
Counts can buy an "Infrastructure package" Which contains the needed roads and buildings. A mayor has to buy each piece individually which costs 20% more. Counts own the county