The Nahegau was in the Middle Ages a county, which covered the environs of the Nahe and large parts of present-day Rhenish Hesse, after a successful expansion of the narrow territory, which did not reach the Rhine, to the disadvantage of the Wormsgau. Among other expansions were Ingelheim in 937, Spiesheim in 960, Saulheim in 973 and Flonheim in 996, until after the end of the expansion the Selz set the southern limit and the limit to the Wormsgau.
The Nahegau was among the central possessions of the Salian dynasty, to which from the mid-11th century the Emichones succeeded. The family of the Emichones divided itself later into the Counts of Veldenz, the Wild- and the Raugraves. Perhaps the Counts of Leiningen descended from the Emichones as well.
Counts in Nahegau were:
- Werner (d. probably 920) Count in Nahegau, Speyergau and Wormsgau ca. 890/910, married NN from the House of the Konradiner
- Conrad der Rote (d. 955), his son, Count in Nahegau, Speyergau, Wormsgau and Niddagau, Count in Franconia, Duke of Lorraine, married ca. 947 Liutgard of Saxony (b. 931, d. 953) daughter of King Otto I (Liudolfinger)
- Otto "of Worms" (d. 1004), his son, Count in Nahegau, Speyergau, Wormsgau, Elsenzgau, Kraichgau, Enzgau, Pfinzgau and Ufgau, Duke of Carinthia
- Conrad II. der Jüngere (b. probably 1003, d. 1039) his grandson, Count in Nahegau, Speyergau and Wormsgau, Duke of Carinthia 1036–1039
- Bauer, Thomas: Geschichtlicher Atlas der Rheinlande, 7. Lieferung, IV.9: Die mittelalterlichen Gaue; 2000; ISBN 3-7927-1818-9