I apologize for taking so long to reply. Yes, Adam died in Leon, Mason County USA in 1900. Thanks for the referral to the find-a-grave site. Unfortunately, that grave marker and information was already known to me. I am not looking for his descendants, I am looking exclusively for his ancestors.
Adam came to America, as far as I can tell, alone. He did not marry until he was in the United States. It is possibly his father's name is William, but that is debatable as different names were listed as his father in various death and marriage certificates. There is no documentation to verify what area of Ireland he came from, however, I have reason to believe it was actually from County Antrim instead of County Down. So, I have searched all the information on ancestry. As far as his ancestors or siblings are concerned there is nothing there. In fact, people who do list his father often have the wrong information listed. I am not as familiar with GRONI, I tried to search it and found nothing. However, this doesn't mean it is not there.
Hopefully, this new information may help. Adam McClure b. 1832(ish) and arrived for permanent residence in the US in about 1854 (based on his US census data). He did not marry Molly Tweed as this was a different Adam McClure. If anyone can help locate his parents or siblings names that would be fantastic. If you need more information please ask what you might need so I can try to get you the answer. I appreciate all your help. Thanks.