The county was created in 1851 and organized in 1861. It is named after the strait between the Door Peninsula and Washington Island. The dangerous passage, which is now scattered with shipwrecks, was known to early French explorers and local Native Americans.
The Door County peninsula has been inhabited for about 11,000 years. Artifacts from an ancient village site at Nicolet Bay Beach have been dated to about 400 BCE. This site was occupied by various cultures until about 1300 CE.
Door County's namesake came from Porte des Morts, anglicized as "Death's Door", or the passage between the tip of the Door County Peninsula and Washington Island. It is a common misconception that the name "Death's Door", or "Porte des Morts", arose from the number of shipwrecks associated with the passage. It was instead the result of Native American tales, heard by early French explorers, related to a failed raid by the Ho-Chunk (Winnebago) tribe to capture Washington Island from the rival Pottawatomie tribe in the early 1600s. A storm arose as the war party was halfway across, capsizing and killing about a third of the Ho-Chunk tribe in the process.
The 18th and 19th centuries saw the immigration and settlement of pioneers, mariners, fishermen and farmers, with the first white settler being Increase Claflin. Economic sustenance came from lumbering and tourism.