Thornmarsh is a region located in Black Marsh. The region has had some involvement in the Ebonheart Pact during the Alliance War of the Second Era. Future Vicecanon Heita-Meen escaped from the House Dres Saltrice Fields to end up in the Marsh. After the Second Akaviri Invasion in central Morrowind, the Pact had formed and some tribes of Black Marsh entered the new Alliance. Tribes from Shadowfen, Murkmire, and Thornmarsh joined the Pact. According to an article, Thornmarsh can be found east of Shadowfen. The city of Thorn can be found here.
- The Elder Scrolls Online (mentioned only)