To aid me in determining a location within the United States I use the GNIS database interface supplied by the Yale Peabody Museum. GNIS is the Geographic Names Information System from the U.S. Geological Survey. You can also use their search interface here: GNIS Feature Search. I prefer the simplicity of the Yale Peabody interface, so it is what I will use in examples here.
Today I had to categorize a link for "Cemetery Index, St. Mary's, Maryland." That is all the information I had from the title and the description given. So, I first indexed it under my Cemeteries category. I want to also index the link in the proper location under United States - Maryland. Using the Yale Peabody GNIS, I entered "St. Mary's" and chose Maryland and ANY FEATURE from the menus.
Ancestry.com - Maps, Atlases & Gazetteers
WorldVitalRecords.com - Search All Historical Maps And Gazetteers Databases