I hope you get this since it's been so long, but I just found this information!
I have been looking for this info because my great great grandmother is recorded as buried in Mortimer in 1917.
According to the "Alabama, Post route map showing post offices with intermediate distances on mail routes in operation on the 1st of January 1928," Mortimer is located 1 1/2 miles just west of McCullough, Escambia County, AL. McCullough still exists. It is located in the northwest portion of the county.
You can find this map at "http://www.archives.state.al.us
Click on "Search Our Collections" --> Maps
From the drop down menu choose "Post Route Maps" and click "next." You may have to click "Next" twice. I do for some unknown reason.
Scroll down to E-006 - Alabama, Post route map showing post offices with intermediate distances on mail routes in operation on the 1st of January 1928 - 1928 - Map.
Click on Map and use the tools to zoom in on Mortimer.
You can also find Mortimer on a 1912 map.
Search Our Collections --> Local government/County records on microfilm --> Alabama Counties. Scroll down to Escambia. Choose "Tracking Your Roots: Escambia County." Choose "1912 map of Escambia County, AL."
This map isn't very accurate, but it does give a general location of Mortimer.
I find it interesting it appears on the 1912 map, but not on the 1913 Soil survey map of Escambia County (U. S. Dept. of Agriculture with the Alabama Dept. of Agriculture and Industries). (Also found in the map section, under counties --> Escambia.), and then appears again on the 1928 Post Route map. It is still on the Postal Route Map, yet the Mortimer Post Office only existed 1900-1919.
We hope to be able to go over there and look around this year.
I hope you get this and it helps!