In ArcMap 10.3 I need to overlay a grid on my data sets where each cell is 1 square mile. I do not need the fishnet using geographic coordinates, just simply a grid of 1 square mile placed over the shapefiles and rasters being used.
You may not need the geographic coordinates of your fishnet but you would still use the fishnet tool to accomplish this. Start the tool and for the cell width and height you should set it to 1609.34 meters. There are several other options available so below is the helpfile for fishnet.