The very first map of the Forgotten Realms was created by Ed Greenwood and mailed in sections to TSR during the late 1980s after he sold the setting to the company for $5000. Years later it ended up hanging in a pub near Madison, Wisconsin. D&D historian Ben Riggs talks about the history of the map on his blog.
www.writerbenriggs.com
The map is known as the "Martin Map" after it was saved by TSR's Forgotten Realms editor, Julia Martin -- Jeff Grubb, the then-custodian of the map -- left TSR in 1995, and left the map in his cubicle. Martin kept hold the map and took it to Seattle when WotC bought TSR.

How the First Map of D&D's Forgotten Realms Ended Up Above a Pub — Ben Riggs
An artifact from D&D history long thought lost has again been found. Behold the Martin Map of the Forgotten Realms!
The map is known as the "Martin Map" after it was saved by TSR's Forgotten Realms editor, Julia Martin -- Jeff Grubb, the then-custodian of the map -- left TSR in 1995, and left the map in his cubicle. Martin kept hold the map and took it to Seattle when WotC bought TSR.