Identifying the cause of decline of a homeowner's tree is difficult if not impossible over the internet, email, or the phone. That being said, premature leaf drop is definitely a tell-tale sign that "something" is wrong, whether the root is environmental (drought, flooding, lightning, soil compaction, herbicide damage, etc.) or biological (insects/disease).
The symptoms may be ephemeral or transient in nature, or they may be more permanent.
Option #1: Reach out to your local UI Extension office to see if they have a horticulturist or Master Gardener/Naturalist available to conduct an on-site visit and assessment.
Option #2: Contact a certified arborist who specializes in tree health issues.
Option #3: Submit a proper sample to the UI Plant Clinic to rule out several common pathogens that affect oak.
Best of luck!