Every now and then you may overlook a crucial detail in one of the sources you have accessed. Several years ago, I was working on my great-grandfather's siblings. I was missing the maiden name of the wife of one of his brothers. I pulled out an old packet on the Prall and Prowell families of York Co., PA. I had been through that source 3-4 times, yet, this time I found the necessary marriage record.
With that in mind, here are some sources you may want to give a 2nd, 3rd or 4th look.
1) Federal and state censuses
2) Military records and pension files
3) Family group records
4) Vital records
6) City and county directories
7) County histories and compiled records
8) Deeds, probate files and court records