My dad is already receiving Medicare and Medicaid in Illinois. If I moved him to California would he be covered or would we have to reapply?

He would have to re-apply for Medicaid, since that is handled by individual states. His basic Medicare A should stay the same though they should be notified about the change of address. If he had Medicare B, supplemental Medicare and Medicare D - in otherwards anything that uses a third party insurance company, he'd need to change that, but since he's on Medicaid, that all should be part of the Medicaid policy. You may want to check with CA Medicaid to see what is required.
Good luck,
Carol

Carol's answer is spot-on, I'd like to add that Medicaid is needs based so if they have assets that are exempt in 1 state that might not hold for the new state. If they have a home, the home is an exempt asset for Medicaid when they are a resident of the state BUT if they moved the home becomes an outright asset; they are no longer are a resident of the old state so do not qualify for Medicaid. Some states will allow for a deferral of 6 months to sell the house (this is not automatic but an individual special circumstances waiver), but all the proceeds from the sale has to go to the state's Medicaid program. My MIL was in a NH in NOLA when Hurricane Katrina came through, her NH took everybody to Houston and got placed in NH facilities there. TX Medicaid did emgency waiver for all on LA Medicaid for months, but eventually those that still had homes back in NOLA had to either move back to a NH somewhere in LA to stay on Medicaid or start to private pay for their TX NH because their home ownership was an asset which put them above Medicaid limit.

How and where to re-apply Medicare and Medicaid in Illinois