According to their Wikipedia article, they are widespread in Canada and the eastern third of the United States. Even so, I'd never encountered one until moving to West Virginia.
The following shots were all taken last weekend at Cooper's Rock state forest. All were taken with a Canon 77D and a vintage Canon FD 50mm f/3.5 Macro lens. In other words, manual settings and manual focusing.
Lady's slippers usually appear in colonies. They are said to prefer pine forests, but I have only seen them in deciduous woods. Lady's slippers have a symbiotic association with a particular fungus. It was thought that the fungus was necessary to provide the plant with nutrients, but recent research indicates that the fungus is only necessary for seed germination.