The name Datça comes from Stadia, an ancient town near Cnidus. Stadia developed into Tadya, Dadya, Dadça, and then Datça.
Both the town and the peninsula of Datça were called Reşadiye for a brief period in the beginning of the 20th century, honoring the penultimate Ottoman Sultan Mehmed V Reşad, and some maps may still refer to the peninsula under this name; today Reşadiye is the name of one of the quarters of the town.
The long and narrow Datça Peninsula, whose outline follows the undulations of small bays and coves facing south or north all along its length which reaches near 100 km (62 mi), corresponds almost exactly to the Datça district, with the addition beyond its isthmus of a small panhandle in the direction of the south-east. The isthmus itself is only several hundred meters wide.
The extreme end of the western tip of the district and the peninsula, the locality called Tekir, is the location of the ancient city of Knidos. There is an ongoing debate on whether or not this location was the original site of the ancient city, a number of sources claiming that until the mid-4th century BCE, Knidos was halfway along the peninsula, near the present-day district center.
The peninsula's eastern end is marked by the fjord-like indentation of Bencik Cove, 1.5 km in length, at the end of which the narrow isthmus where it joins the mainland is found. This point is a natural curiosity which offers a wide view of the Gulf of Gökova in the north and the Gulf of Hisarönü in the south and is called Balıkaşıran (literally, the place where fish may leap across) and is also often used for the portage of small boats. According to Herodotus, during the Persian invasions in 540 BC, the Knidians had sought to dig a canal at this spot as a defensive measure and in order to transform their territory into an island. But an oracle was consulted who reportedly said "If the gods had so willed, they would have made your land an island. Do not pierce the isthmus." Whereupon they surrendered to the Persians.