Experts and BHG readers answer.
Dying holly tree
I assume you have checked the soil around it for any problems. Could it have been hit by salt, weed killer or weed wacker by accident? Is there any damage to the main trunk -eg. gnawed by rabbits or rubbed by deer antlers. Check at soil level to see if it is still in a metal basket with string round the trunk. Often trees are planted incorrectly and several years later there is plastic string or wire left to strangle the plant where till that time all seemed to be well. The tree often grows over wire or string that does not rot down. If so dig the tree and remove the strangler, replanting carefully in good soil and giving tender loving care till the plant gets back on its feet. I would advise calling your local cooperative extension office (yellow or blue pages). They may arrange for a site visit or otherwise give you advice for no fee.