Tulcea County is a county (județ) of Romania, in the historical region Dobruja, with the capital city at Tulcea. It includes in its northeast corner the large and thinly-populated estuary of the Danube.

The Danube Delta is the second largest river delta in Europe, after the Volga Delta, and is the best preserved on the continent. The greater part of the Danube Delta lies in Romania, with a small part in Ukraine. Its approximate surface area is 4,152 square kilometres, of which 3,446 km2 (1,331 sq mi) is in Romania. With the lagoons of Razim–Sinoe, located south of the main delta, the total area of the Danube Delta is 5,165 km2 (1,994 sq mi). The Razim–Sinoe lagoon complex is geologically and ecologically related to the delta proper; the combined territory is listed as a World Heritage Site.