In 1680, Louis XIV of France gave orders to build a fortification (to defend the new French eastern frontier) on the banks of the river Saar which was called Sarre-Louis.

In 1697, the Treaty of Ryswick made most parts of Lorraine independent again, but Saarlouis and the surrounding areas remained a French exclave.

Marshal Michel Ney, who was born in Saarlouis, was arrested and tried for treason after the failure of Napoleon I's Waterloo Campaign.

As a result, anti-Nazi groups campaigned heavily for the Saarland to remain under control of League of Nations as long as Adolf Hitler ruled Germany.

Over time, the following districts have been incorporated into Saarlouis: Even today, the fortress dominates the town's hexagonal floor plan.

After 1887, some parts of the fortress were slighted, but many buildings and places, e.g. the casemates, some barracks and the Great Market with the Commander's Office and the Vauban island, a former ravelin with a memorial for Michel Ney can still be seen today.

The plant in the Roederberg suburb opened in 1970, but in 2022 is threatened with closure when the Ford Focus production cycle runs out in 2025.