Hog Island, at 2 acres in size, is the lone component of the Green Bay National Wildlife Refuge. The island is located in Lake Michigan, east of Washington Island, in Door County, Wisconsin. The island was set aside by Executive Order in 1913 as a preserve and breeding ground for native birds. Along with Gravel Island National Wildlife Refuge, Green Bay Refuge makes up the Wisconsin Islands Wilderness Area. The refuge is managed by staff at Horicon National Wildlife Refuge, in Mayville, WI.

At one time, Hog Island was tree-covered. However, all the trees are now dead, and many have fallen over. The island supports a nesting colony of herring gulls, double-crested cormorants, and a few red-breasted mergansers.

No development has occurred on the island due to its small size, remoteness, and landing difficulties. All public use is restricted due to ground nesting by migratory birds and the limited and treacherous access.