Where Should I Grind For The Corrupted Keys?

I would prefer coords of good spawn locations.

 

There are not really exact coords as the key guardians don't spawn at a single point but spread over a region. The guardians for Decrepit Sewers spawn in the Kander Forrest and the ones for the Infested Pit spawn in the Light Forest.

 

For the Corrupted Decrepit Sewer keys, I found that the guardians spawn often around a graveyard at (-737, -5465). The graveyard is north of the church and contains a mob called "Shade". Nii Guardians also spawn frequently in this area, and you can typically get about 3 runes for every key you obtain (each key requires 3 runes to be reforged, so this acts as a good farming area for corrupted dungeons).

As for the Corrupted Infested Pit keys, I have not found a good "farming" location for the keys. My only advice I can give you is to stay on the Light Forest path and walk down it several times. Typically, the guardian will run at you fast when in range, so walking down the path is fairly efficient and it protects you from the annoying pools filled with hostile mobs.