Liquid Wrench or PBlaster will do a better job of freeing the cylinder. They often freeze in the winter due to dirt plus a little water. Once you get it freed up, then use some WD-40 to lube.

To prevent this problem, spray twice a year with Mobil 1 Spray Lube or Superlube Spray, placing the spray tube right into the lock cylcinder and then working it back and forth with the key. Neither spray attracts dirt and both are good lubricants.