Thom, welcome to WikiTree and G2G.
The parents of Matilda Mueller were Chas and Matilda Mueller. Chas was born in Belgium and Matilda was born in Germany.
The family was living in IL on 1880 according to the 1880 US Census. Please see lines 4 to 7 in the following image (Last name is spelled Miller):
The family moved to MO before 1900. They were living in Kansas City on 1900. They are listed at the very bottom of the following 1900 US Census sheet:
Roy Otis Rinehart was the son of Charles Rinehart born in OH and Jane born in IL. The family was living in KS on 1880. They are listed in lines 35 to 39 on the following 1880 US Census sheet:
Roy was living in Kansas City on 1900. He is listed as a "Roomer" in the following 1900 US Census sheet (Line 91):
So your grandparets met each other in Kansas City. They were married and living there on 1920. They are listed in lines 37 and 38 in the following 1920 US Census sheet: