The Emerald Ash Borer has killed on the order of 6 million ash trees in the region of the major outbreak, mainly the Michigan Lower Peninsula. For now, the major outbreak is confined to Michigan and some surrounding areas of Canada, Indiana, and Ohio. An outbreak in Maryland and Virginia resulting from an illegal shipment of infected nursery stock seems to have been contained. The control method currently used is to remove and dispose of every ash tree within a half-mile of an infested tree since there is no reliable test for infestation. USDA has quarantined 13 counties in southeastern Michigan.
Two useful websites are:
This site is maintained by the USDA Forest Service. It gives current information on the status of this threat.