The name Montmorency was recorded for the first time in Medieval Latin as Mons Maurentiacus (attested in 993).
Mons Maurentiacus, literally "Mount Maurentiacus", was the name given to the promontory over which a castle was built in the Early Middle Ages.
Maurentiacus, the name of the area surrounding the promontory, meant "estate of Maurentius", probably a Gallo-Roman landowner.

In 1689 Montmorency was officially renamed Enghien (read history section below), but the village on the slopes of the promontory was still referred to as "Montmorency" by most people.

Indeed, during the French Revolution, at the creation of French communes in 1790, the newly born commune was named Montmorency.
Three years later in 1793, at the peak of the French Revolution, the name of the commune, which was probably thought of as too reminiscent of the overthrown Ancien Régime, was changed into Émile, in honor of French philosopher and writer Jean-Jacques Rousseau who had composed his educational treaty Émile a few decades earlier while in residence at Montmorency.

In 1813 the commune was renamed Montmorency.
In 1815, at the Restoration of monarchy, the commune was renamed Enghien.
Throughout these troubled years, however, the village was always referred to as "Montmorency" by the locals, regardless of what the official name was in all its changes.

The name "Enghien", on the other hand, was used for the lake and marshland in the valley beneath Montmorency, an area that was withdrawn from the jurisdiction of the commune of Montmorency/Enghien in 1790, and was divided between the jurisdictions of several neighboring communes.
In other words, the place called "Enghien" was not located within the commune of Enghien.

This confusing situation was ended on 27 November 1832, when the commune of Enghien was definitely renamed Montmorency.
In 1850, the area of Enghien, which had developed as a spa resort, was incorporated as a commune (named Enghien-les-Bains) by detaching its territory from the territory of four communes neighboring Montmorency.
The commune of Montmorency did not lose territory and as such was not affected by the incorporation of the commune of Enghien-les-Bains.
The name Montmorency was recorded for the first time in Medieval Latin as Mons Maurentiacus (attested in 993). Mons Maurentiacus, literally "Mount Maurentiacus", was the name given to the promontory over which a castle was built in the Early Middle Ages. Maurentiacus, the name of the area surrounding the promontory, meant "estate of Maurentius", probably a Gallo-Roman landowner.
In 1689 Montmorency was officially renamed Enghien (read history section below), but the village on the slopes of the promontory was still referred to as "Montmorency" by most people.
Indeed, during the French Revolution, at the creation of French communes in 1790, the newly born commune was named Montmorency. Three years later in 1793, at the peak of the French Revolution, the name of the commune, which was probably thought of as too reminiscent of the overthrown Ancien Régime, was changed into Émile, in honor of French philosopher and writer Jean-Jacques Rousseau who had composed his educational treaty Émile a few decades earlier while in residence at Montmorency.
In 1813 the commune was renamed Montmorency. In 1815, at the Restoration of monarchy, the commune was renamed Enghien. Throughout these troubled years, however, the village was always referred to as "Montmorency" by the locals, regardless of what the official name was in all its changes.
The name "Enghien", on the other hand, was used for the lake and marshland in the valley beneath Montmorency, an area that was withdrawn from the jurisdiction of the commune of Montmorency/Enghien in 1790, and was divided between the jurisdictions of several neighboring communes. In other words, the place called "Enghien" was not located within the commune of Enghien.
This confusing situation was ended on 27 November 1832, when the commune of Enghien was definitely renamed Montmorency. In 1850, the area of Enghien, which had developed as a spa resort, was incorporated as a commune (named Enghien-les-Bains) by detaching its territory from the territory of four communes neighboring Montmorency. The commune of Montmorency did not lose territory and as such was not affected by the incorporation of the commune of Enghien-les-Bains.
Montmorency, Val-d'Oise