Do you mean in a particular country? Because in the UK, there are two Duchies (Lancaster, held by the Queen, and Cornwall, held by her eldest son), which are both quite large and earn a lot of money from rent. Not to mention of course, there are many Barons and some other Dukes, and the title can be referred to as a Barony (ie "the Barony was passed down to his son") even though it doesn't actually give any particular rights to land (for example, the Duke of Edinburgh is a titular rank with no particular power or land in Edinburgh; it's just named after Edinburgh).Although you could ask why County is a division used by the government for the purpose of local government administration, while the two Duchies are land-owners, and baronies are positions, or potential positions post-1997, in the national government (specifically the House of Lords).