Here is a nice corn growing degree day (GDD) tool for the US available from Nutrien at Nutrien GDD Tool (ag-wx.com). You can input the location, planting date, and maturity level and get a curve that shows the corn development stage. It is based on PRISM gridded weather data developed by Oregon State University. Some of you might find it useful. The chart below shows a sample curve for Tifton GA.