I need advise

Hi, my name is Kathy Runyan. All my life I have wanted to know who my Father's birth parents were. He promised to give me the information after my Grandmother passed away. Well, sadly, that day came last December. But, even sadder is the fact that my Father passed away 2 weeks later leaving no information. We were still grieving my Grandmother at that time so pushing for this information from my Father didn't cross my mind before he passed. I don't know what to do. I don't know if I have any rights as an adptees daughter to find this information after everyone involved has passed on. I know that he was born in Michigan. I know his given name at birth and birthdate. Can someone help me? Thanks, Kathy