Belle Island has 42,775,920 sq ft of total area. There are 6,104,916 sq ft of water from the two ponds and 3 lakes. That leaves 34,993,352 sq ft of land, which would give all 713,777 Detroiters room to be on the island at one time. Each resident would get 49 sq ft – about the size of a picnic table. If you took all 9,883,640 Michiganders and placed them on the island, each citizen would get 3.5 sq ft, which is approximately the shoulder-to-shoulder density at concerts.
If every member of the United States lived in an area with the population density of Brooklyn, NY (35,000 per sq mi) we all could fit into New Hampshire, the 5th smallest state.