洛因（德语：Leun）是德国黑森州的一个市镇。总面积28.66平方公里，总人口5770人，其中男性2841人，女性2929人（2011年12月31日），人口密度201人/平方公里。

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Leun is a small town in the Lahn-Dill-Kreis in Hesse, Germany.

Leun lies some 10 km west of Wetzlar between the foothills of the northern Taunus and the Westerwald in the Lahn valley, at a height of 150 to 330 m above sea level.

Leun borders in the north on the communities of Greifenstein and Ehringshausen, in the east on the town of Solms, in the south on the town of Braunfels (all in the Lahn-Dill-Kreis) and in the west on the community of Löhnberg (Limburg-Weilburg).