If I remember correctly, there is a book at Greater Canonsburg Public Library on the MacMillan family & again if I remember correctly, there is some of the writing in it from John MacMillans Diary. And I agree with you that he listed marriages, baptisms, etc. but gave no names. It is indeed frustrating. You might be able to get a copy through inter library loan but usually these kinds of books are non-circulating. It's worth a try.