When a wealthy landowner died and the land was known to belong to the crown,  Inquisitions Post Mortem were held in order to discover what income and rights were due to the crown and who the heir should be 
Those who held land directly on the Crown’s behalf were known as tenants in chief and if they  died without an heir, the land ownership defaulted to the Crown. If there was an heir, the Crown kept the lands until a payment had been made in order to assume possession.
In the event that the heir was under age - 21 for men or 14 for women -the Crown kept the lands until they came of age and received rights of wardship and marriage, collecting the revenues of the estate and disposing of the heir in marriage. The Crown was able to sell these rights to third parties, who were not necessarily the next of kin. 
The Inquisition Return contains-  

• the County
• The name of the officer
• A list of the jurors
• The name of the deceased and the date of their death
• A brief description of each landholding
• It’s value (which was often underestimated)
• The tenure by which it was held

These records can be found at the National Archives for England & Wales and the Genealogical office, Dublin for Ireland. Some Abstracts have been published by County Record Offices and Societies.

Ireland can be found here 

They have been microfilmed by the The Church of Jesus Christ of Latter-day Saints and are available at their Family Search History Centres