The Carolinas
The plural of the proper noun is Carolinas. It can be used to refer to North and South Carolina as a region.
The singular form is bacillus (one organism, or one type of organism). The plural is bacilli. Examples: He could clearly see the shape of the bacillus. This bacillus is common in tropical climates. Bacilli were found in his spleen. Various bacilli are endemic to the region.
North Carolina is in the Southern Region.
The region of the Carolinas is the south-eastern states.
The plural possessive is regions'.
the piedmont region
The Piedmont region.
Regions'
A herd of antelope regularly usesthis water hole. (singular)Many herds of animals regularly usethis water hole. (plural)
Caribou is the animal. Cariboo is a region in central British Columbia. Caribou is both singular and plural, as in "I saw a caribou." and "I saw five caribou." Other game species such as deer, elk and grouse also follow this convention.
Virginia, Georgia, South Carolina, and North Carolina
North Carolina is in the Southeast region of the United States.