As the name suggests, the eastern gray squirrel has predominantly gray fur, but it can have a brownish color. It has a white underside and a large bushy tail. Particularly in urban situations where the risk of predation is reduced, both white- and black-colored individuals are quite often found. The melanistic form, which is almost entirely black, is predominant in certain populations and in certain geographic areas, such as in large parts of southeastern Canada. Genetic variations within these include individuals with black tails and black-colored squirrels with white tails (see Tree squirrel for more information on these color variations).
The head and body length is from 23 to 30 cm (9.1 to 12 in), the tail from 19 to 25 cm (7.5 to 9.8 in) and the adult weight varies between 400 and 600 g (14 and 21 oz).
The tracks of an eastern gray squirrel are difficult to distinguish from the related fox squirrel and Abert's squirrel, though the latter's range is almost entirely different from the gray's. Like all squirrels, the eastern gray shows four fingers on the front feet and five on the hind feet. The hind foot-pad is often not visible in the track. When bounding or moving at speed, the front foot tracks will be behind the hind foot tracks. The bounding stride can be two to three feet long
Like many members of the family Sciuridae, the eastern gray squirrel is a scatter-hoarder; it hoards food in numerous small caches for later recovery. Some caches are quite temporary, especially those made near the site of a sudden abundance of food which can be retrieved within hours or days for reburial in a more secure site. Others are more permanent and are not retrieved until months later. Each squirrel is estimated to make several thousand caches each season. The squirrels have very accurate spatial memory for the locations of these caches, and use distant and nearby landmarks to retrieve them. Smell is used once the squirrel is within a few centimeters of the cache.
The eastern gray squirrel is one of very few mammalian species that can descend a tree head-first. It does this by turning its feet so the claws of its hind paws are backward pointing and can grip the tree bark.
Eastern gray squirrels eat a range of foods, such as tree bark, berries, many types of seeds and acorns, walnuts, and other nuts, and some types of fungi found in the forests, including fly agaric mushrooms. On very rare occasions, when their usual food sources are scarce, eastern gray squirrels will also prey upon insects, frogs, small rodents including other squirrels, and small birds, their eggs and young. They will also gnaw on bones, antlers, and turtle shells – likely as a source of minerals sparse in their normal diet.
The eastern gray squirrel is found in the eastern United States and adjacent southern Canada; New Brunswick to Manitoba, south to East Texas and Florida. It has also been introduced into Ireland, Britain, Italy, South Africa, and Australia
In the wild, eastern gray squirrels can be found inhabiting large areas of mature, dense woodland ecosystems, generally covering 40 hectares of land. These forests usually contain large amounts of dense understory vegetation that provides them sufficient amount of food sources and favorable shelters. Oak-hickory hardwood forests are preferred over coniferous forests.
Eastern gray squirrels generally prefer constructing their dens upon large tree branches and within the hollow trunks of trees. They also have been known to take shelter within abandoned bird nests. The dens are usually lined with moss plants, thistledown, dried grass, and feathers. These perhaps provide and assist in the insulation of the den, used to reduce heat loss. A cover to the den is usually built afterwards.