Mers-les-Bains does not have much history. There are one or two noble families known to have been seigneurs of places within the commune; The coat-of-arms, carved in stone, of the Mython family of Froideville adorns one of the Mayor's offices today. The Lucas family of Rompval, the Lattaignant seigneurs of Blengues, and the Torcy family, seigneurs of Mers-les-Bains are all mentioned in archives. Some parts of their coat-of-arms can still be seen today, as part of the official badge of the town, adopted in December 1962.
Once just a small fishing port, the seaside ‘bathing station’ grew partly because of the railway line that ran from Paris to Tréport. Entire families could make the 3 hour journey from Paris to discover the benefits of bathing and breathe the fresh, iodized air. Many would eventually buy land and build sumptuous second homes in the town.