2014 Federal Corporate, S-Crop and Partnership Tax Returns for Tax Extension filers 2014 Federal Corporate, S-Crop and Partnership Tax Returns for Tax Extension filers September 15, 2015 September 15, 2015: Last day to file the 2014 Federal Corporate, S-Crop and Partnership Tax Returns for Tax Extension filers More about 2014 Federal Corporate, S-Crop and Partnership Tax Returns for Tax Extension filers