With some very clever help from the Genealogy Circle of Munster, I have at long last found the answer to this question.

Gregoire was NOT born in Munster, but rather in the Bas-Rhin town of Ohnenheim.

His father, Georg Jacob Roth, had emigrated to Ohnenheim in 1798 from the town of Kindsbach near Kaiserslautern Germany and married Anna Maria Holl of Ohnenheim in 1800. In addition to Gregoire, they had 5 other children all born in Ohnenheim: Benoit (1838), Jean (1839), Julienne (1845), Catherine (1847) and Marie Anne (1851 - she passed away 10 days after birth).