text: Followup - The city does have a detailed mapping application, which does show the city limits... I guess I have answered my own question. I just need to reference this map and edit the boundary accordingly. Link to the map for anyone interested:
  https://decatur.maps.arcgis.com/apps/webappviewer/index.html?id=78eb93be3c4b4b9faef958f98c0a85c8