Mont-Tonnerre [mɔ̃.tɔ.nɛʁ] was a department of the First French Republic and later the First French Empire in present-day Germany. It was named after the highest point in the Palatinate, the Donnersberg. It was the southernmost of four departments formed in 1798 when the west bank of the Rhine was annexed by France. Prior to the French occupation, its territory was divided between the Archbishopric of Mainz, the Bishopric of Speyer, the Bishopric of Worms, Nassau-Weilburg, Hesse-Darmstadt, the Electorate of the Palatinate and the imperial cities of Worms and Speyer. Its territory is now part of the German states of Rhineland-Palatinate and Saarland. Its capital was Mainz (French: Mayence).
- Mainz, cantons: Alzey, Bingen, Bechtheim, Kirchheimbolanden, Mainz (2 cantons), Nieder-Olm, Ober-Ingelheim, Oppenheim, Wöllstein and Wörrstadt.
- Kaiserslautern (French: Kayserslautern), cantons: Göllheim, Kaiserslautern, Lauterecken, Obermoschel, Otterberg, Rockenhausen, Winnweiler and Wolfstein.
- Speyer (French: Spire), cantons: Dürkheim, Edenkoben, Frankenthal, Germersheim, Grünstadt, Mutterstadt, Neustadt, Pfeddersheim, Speyer and Worms.
- Zweibrücken (French: Deux-Ponts), cantons: Annweiler, Homburg, Landstuhl, Medelsheim, Neuhornbach, Pirmasens, Waldfischbach and Zweibrücken.
Its population in 1812 was 342,316.