Mid Down was a constituency of the Parliament of Northern Ireland.
It was created when the House of Commons (Method of Voting and Redistribution of Seats) Act (Northern Ireland) 1929 introduced first-past-the-post elections throughout Northern Ireland.
The constituency survived unchanged until 1969, when it was considerably reduced in size, with areas of the seat being transferred to Lagan Valley and North Down.
The seat comprised parts of the rural districts of Castlereagh, Hillsborough and Newtownards.
It was only contested on one occasion, by a Northern Ireland Labour Party candidate who received only 23% of the votes cast.