look for insects in these bare spots. European cranefly, chafer or billbug larvae... all three live in the soil. Cut a 1-foot square sample to the depth of 2" and flip it over. If grubs are present (5 or more per sq ft) apply a lawn insecticide to help with the issue. 

Let me know what you find...

Alec 

We didn't find any grubs and the whole lawn has big dead spots all over. Like a disease is taking over. It gets plenty of water.  

It could be necrotic ring spot or summer patch.  Both are root pathogens that feed on Kentucky bluegrass. Send us a sample for identification, no charge...

Diagnostic Lab | College of Agricultural Sciences (oregonstate.edu)

Necrotic ring spot or summer patch pressure can be reduced with fall or spring core cultivation. This reducing the organic matter the pathogen can feed on during the cool weather when the turfgrass is not stressed. Applying a systemic fungicide (with the active ingredients propiconazole, azoxystrobin or both) in the fall and spring.