Not to bring up legalities, but did he actually live there? if not, are you on the lease? or is he on the lease?
The probation officer would need a warrant to search your property. If he could not verify who the legal lease-holders are, it is up to him to find out.
I do not know the details of the case nor am I a lawyer, but it sounds like you have a case against the county / state.
Amendment IV
The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no warrants shall issue, but upon probable cause, supported by oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized.