These centres had already had a bond lasting from the Middle Ages to the early 19th century when they were all in the Electorate of the Palatinate’s Aicher Cent (tithing area).

The Electorate of the Palatinate’s and Mainz’s overlordship in the area lasted until 1802, when under the Reichsdeputationshauptschluss they all became part of the Grand Duchy of Hesse.

The village, whose livelihood originally came from craftsmen and farmers, experienced an upswing in the 19th century owing to the boom in new red sandstone processing.

Today’s open-air resort (Luftkurort) of Hammelbach is, with some 1,400 inhabitants, the biggest and oldest of Grasellenbach’s constituent communities, as well as its administrative seat.

Hammelbach has been historically regarded as the only constituent community that may legitimately hold a kermis, as that is where the Evangelical church stands.

Tromm is, with some 100 inhabitants, the smallest and highest of Grasellenbach's constituent communities, and lies on the like-named mountain ridge (577 m above sea level at its peak) among meadows and woods.

At the Tromm conference houses at the Karl Kübel Foundation's Odenwald Institute, there are regular seminars on the themes of job, family, communication and personal development.

The municipal election held on 26 March 2006 yielded the following results: Markus Röth has been mayor of Grasellenbach since 1997.

Buslines run to the railway stations in Heppenheim and Weinheim, which, just like Grasellenbach, belong to the Rhine-Neckar Transport Network (Verkehrsverbund Rhein-Neckar).