The Twin Valley was a "valley of peace" for the various Indian tribes hunting here. The Shawnees had a settlement nearby as late as 1804. The first pioneers arrived in the area in 1798 and stayed about six years before most moved on. Germantown was settled in August, 1804, by German-speaking families from Pennsylvania. They were led by Philip Gunckel, the only original settler who spoke English. He selected the Twin Valley as a site for a grist mill. The German language was spoken in Germantown until the early 1900s. Mr. Gunckel established the first plat in 1814. The Village incorporated in 1833 and the population had grown to 1200 by 1840.

Those buildings and homes of a historical interest have been documented by an active historical society, founded in 1973. Six area buildings, as well as the entire downtown business section, have been designated Montgomery County Landmarks: the I00F Lodge building, the K of P Lodge building, the Rohrer Mansion, the old Shuey Mill, and both the Mudlick Homestead and the old Mudlick School.

In May 1976, the downtown core, known as the " Gunckel Town Plat " was recognized by the National Historical Park Service of the U.S. Department of the Interior as a National Historic Site and Historical Preservation District. Also attaining national recognition were the Shuey Mill, the Poast House, and the Watson (Rohrer) House.

June 8, 1976 - A council-manager form of government was adopted.

1980 - Germantown became a city.