Sometimes a baby squirrel will fall out of its nest. Usually, the mother will retrieve it as long as the baby is warm and healthy. Try reuniting the squirrel with its mother.
To try to reunite a squirrel baby with its mother, put it in a small box it cannot climb out of, and attach it to the trunk of the tree a few feet off the ground. Do not cover the baby with any bedding. It is very important to keep the baby warm—the mother will not retrieve a cold baby. You can fill a small soda pop bottle with hot water, wrap it in a towel, and brace it inside the box. Replace the hot water frequently as it cools down. Leave the area and monitor from a distance—the mother will not return if there are people or pets around. If the mother has not retrieved the baby within a couple of hours, it might need rescuing. Never leave a baby squirrel out overnight since the mother will not retrieve it after dark. Bring the squirrel inside for the night to keep warm and put the box back outside first thing in the morning.