Legal Definition of Ancillary administration: A proceeding in a locality where a deceased person owned property, but which is a different locality from the one in which the estate is being administered | Learn about ancillary administration and its importance in the proper distribution of assets owned in different localities. Discover real-life examples and why this legal proceeding is crucial for business owners. Consult a qualified attorney who specializes in probate and estate planning to navigate the ancillary administration process effectively