What is the difference between a jackrabbit, a hare, and a rabbit?

Jackrabbits are hares. Hares have large, long ears, long legs, and a larger body than rabbits.

The whitetail jackrabbit is the largest hare in the Great Plains, having a head and body length of 18 to 22 inches (46 to 56 cm) and weighing 5 to 10 pounds (2.2 to 4.5 kg). It is brownish gray in summer and white or pale gray in winter. The entire tail is white. The blacktail jackrabbit, somewhat smaller than its northern cousin, weighs only 3 to 7 pounds (1.3 to 3.1 kg) and is 17 to 21 inches (43 to 53 cm) long. It has a grayish-brown body, large black-tipped ears, and a black streak on the top of its tail.

The snowshoe hare is 13 to 18 inches (33 to 46 cm) long and weighs 2 to 4 pounds (0.9 to 1.8 kg). It has larger feet than the whitetail and blacktail jackrabbits. The snowshoe turns white in winter and is a dark brown during the summer. Its ears are smaller than those of the other hares. The antelope jackrabbit is 19 to 21 inches (48 to 53 cm) long and weighs 6 to 13 pounds (2.7 to 5.9 kg). Its ears are extremely large and its sides are a pale white. The European hare is the largest of the hares in the Northeast, weighing 7 to 10 pounds (3.1 to 4.5 kg) and reaching 25 to 27 inches (63 to 68 cm) in size. This nonnative hare is brownish gray year round.

Resources: (online)
Cottontails
Jackrabbits