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.