Hi Kathryn, 

The symptoms are difficult to see in the photos. Based on the holes, Emerald Ash Borer (EAB) is the most likely suspect given how extensively they have impacted ash trees in the entire region. It's possible more than one culprit is causing the ash's decline, and perhaps an environmental stress factor first predisposed the ash to attack. While we can't see much detail in the photos, you can compare what you see in person to the information on this page: https://extension.umd.edu/resource/emerald-ash-borer-eab

We suggest you have a certified arborist assess the tree, especially since they can evaluate the likelihood preventative EAB treatments will have any value. If an insecticide is warranted, a certified pesticide applicator would need to apply it. Re-treatments will be needed to maintain protection, so the costs of this will need to be weighed against the one-time cost of tree removal, particularly if the arborist deems the tree a hazard due to existing damage. You will note that once dead this tree loses structural integrity quickly and should be removed promptly before it becomes a fall hazard.

This resource from Perdue might help you decide how to proceed: https://extension.entm.purdue.edu/EAB/PDF/NABB_DecisionGuide.pdf. 

Jamie