Tønder County (Danish: Tønder Amt) is a former province in Denmark, located the south-western part of Southern Jutland. Tønder County was established in 1920 following the reunification of Denmark with South Jutland following the Schleswig Plebiscites. It was dissolved in 1970 when the bulk of the county merged with three other counties to form South Jutland County. Tønder County corresponded geographically to the northern part of the former Prussian Kreis Tondern except for Hviding Herred, which had been part of Kreis Hadersleben. Kreis Tondern had in turn been established in 1867 in order to simplify the intricate administrative structures of the Duchy of Schleswig, and was formed from regions belonging to Ribe County (exclaves of Denmark) and Løgumkloster County (parts of Schleswig).
The southern part of Kreis Tondern remained German and became Kreis Südtondern, with the seat transferred to Niebüll. In 1970, Kreis Südtondern merged into Kreis Nordfriesland.
