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, known as Death's Door, is now scattered with shipwrecks, and 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 name 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.
During the 19th century, various groups of Native Americans occupied the area that would become Door County and its islands. Beginning in mid-century, these Indians, mostly Potawatomi, were removed from the peninsula by the federal government under the Indian Removal Act of 1830. Later in the 19th century, a fairly large-scale immigration of Belgian Walloons populated a small region in southern portion of the county.
A Civilian Conservation Corps camp was established at Peninsula State Park during the Great Depression. In the summer of 1945, Fish Creek was the site of a German POW camp, under an affiliation with a base camp at Fort Sheridan, Illinois. The prisoners engaged in construction projects, cut wood, and picked cherries in Peninsula State Park and the surrounding area. Eagle Bluff Lighthouse was constructed in Peninsula State Park in 1868 on orders from President Andrew Johnson, at a cost of $12,000. It was restored by the Door County Historical Society in 1964, and opened to the public.