After the French defeat in the Franco-Prussian War of 1870-1871, the northeastern part of the Meurthe département was annexed to the German Empire by the Treaty of Frankfurt. On May 18, 1871, about one-third of the Meurthe, corresponding approximately to the arrondissements of Château-Salins and Sarrebourg in the northeast of the département, were detached from Meurthe and annexed to the German Department of Lorraine, becoming part of the Reichsland of Alsace-Lorraine.
The remaining two thirds of Meurthe were merged with one fifth of the Moselle département (arrondissement of Briey, in the extreme west of Moselle, to the northwest of Meurthe) which had escaped German annexation, and on September 7, 1871, the merger gave birth to the new Meurthe-et-Moselle département (area: 5,246 km², compared to 6,070 km² for the former Meurthe), with its préfecture at Nancy.
In 1919, with the Allied victory in the First World War, Alsace-Lorraine was returned to France by Germany at the Treaty of Versailles. However, the old départements of Meurthe and Moselle was not recreated by reverting to the old département borders of before 1871. Instead, Meurthe-et-Moselle was left untouched, and the third of Meurthe and the four fifth of Moselle that had been formed the German Region of Lorraine in 1871 were restituted as the new département of Moselle, whose name is the same as the old département of Moselle but whose borders are quite different.
At the 1866 French census, the Meurthe département had a population of 428,387 inhabitants. In 1872, after the annexation and merger, the new Meurthe-et-Moselle département had a population of 365,137 inhabitants.
At the 1999 French census, if Meurthe still existed it would have had a population of 647,307 inhabitants. On the other hand, in 1999 Meurthe-et-Moselle had a population of 713,779 inhabitants (the industrial area of Briey and Longwy merged in 1871 is more populated than the rural areas of Château-Salins and Sarrebourg lost in 1871).