How many groundhogs live in one hole on average?

Groundhogs excavate a complex, multi-chambered burrow system in which the total length of tunnels can measure up to 65 feet. For a greater part of the year, burrow occupancy is limited to one groundhog per unit. Exceptions occur when males visit the burrows of females during a late winter breeding season, and consequently, following a 32-day gestation period, when females give birth to four to six kits. After approximately a dozen weeks of rapid development, these young disperse from their maternal burrow to dig their own lodging.

Source: Carnegie Museum of Natural History