HESSE-NASSAU (Ger. Hessen-Nassau), a province of Prussia, bounded, from N. to E., S. and W., successively by Westphalia, Waldeck, Hanover, the province of Saxony, the Thuringian States, Bavaria, Hesse and the Rhine Province. There are small detached portions in Waldeck, Thuringia, &c.; on the other hand the province enclaves the province of Oberhessen belonging to the grand-duchy of Hesse, and the circle of Wetzlar belonging to the Rhine Province. Hesse-Nassau was formed in 1867–1868 out of the territories which accrued to Prussia after the war of 1866, namely, the landgraviate of Hesse-Cassel and the duchy of Nassau, in addition to the greater part of the territory of Frankfort-on-Main, parts of the grand-duchy of Hesse, the territory of Homburg and the countship of Hesse-Homburg, together with certain small districts which belonged to Bavaria. It is now divided into the governments of Cassel and Wiesbaden, the second of which consists mainly of the former territory of Nassau (q.v.).
The province has an area of 6062 sq. m., and had a population in 1905 of 2,070,052, being the fourth most densely populated province in Prussia, after Berlin, the Rhine Province and Westphalia. The east and north parts lie in the basin of the river Fulda, which near the north-eastern boundary joins with the Werra to form the Weser. The Main forms part of the southern boundary, and the Rhine the south-western; the western part of the province lies mostly in the basin of the Lahn, a tributary of the Rhine. The province is generally hilly, the highest hills occurring in the east and west. The Fulda rises in the Wasserkuppe (3117 ft.), an eminence of the Rhöngebirge, the highest in the province. In the south-west are the Taunus, bordering the Main, and the Westerwald, west of the Lahn, in which the highest points respectively are the Grosser Feldberg (2887 ft.) and the Fuchskauten (2155 ft.). The congeries of small groups of lower hills in the north are known as the Hessische Bergland.
The province is not notably well suited to agriculture, but in forests it is the richest in Prussia, and the timber trade is large. The chief trees are beech, oak and conifers. Cattle-breeding is extensively practised. The vine is cultivated chiefly on the slopes of the Taunus, in the south-west, where the names of several towns are well known for their wines—Schierstein, Erbach (Marcobrunner), Johannisberg, Geisenheim, Rüdesheim, Assmannshausen. Iron, coal, copper and manganese are mined. The mineral springs are important, including those at Wiesbaden, Homburg, Langenschwalbach, Nenndorf, Schlangenbad and Soden. The chief manufacturing centres are Cassel, Diez, Eschwege, Frankfort, Fulda, Gross Almerode, Hanau and Hersfeld. The province is divided for administration into 42 circles (Kreise), 24 in the government of Cassel and 18 in that of Wiesbaden. It returns 14 representatives to the Reichstag. Marburg is the seat of a university.