Brown Spots on Hydrangea Plant
Good afternoon. This looks like Cercospora leaf spot, a fungal disease that is somewhat common to hydrangea. Here is a link to information on diagnosis and management http://extension.psu.edu/pests/plant-diseases/all-fact-sheets/hydrangea-diseases; here you can see a photo of, and information regarding, the leaf spot I've suggested and just how similar it is to the photo you've submitted.
UD Cooperative Extension also has a plant diagnostic clinic and you can submit a plant sample for evaluation. Information regarding this service and sample submission can be found here: http://extension.udel.edu/ag/plant-diseases/ud-plant-diagnostic-clinic/.
Thank you very much for your quick reply. Hopefully with your diagnosis and the information provided I will be able to assist in restoring this plant to good health so that it can grow into the big, beautiful plant I envision it will be some day. Any other tips you may have in caring for hydrangea would be appreciated.