Work in the mills brought many immigrants to Rockville, particularly during the Civil War expansion period, 1860-1875, when many German immigrants arrived and new businesses catering to the German community opened along Village Street.
Today, most of the city has been designated as the Rockville Historic District."
And so I found an 1895 map of Rockville and located where Charles Pfunder and William Pfunder lived according to the census.
I labeled the surrounding buildings and marked their approximate location with the yellow square:
I am assuming now, that the mill they worked at would be the Springville Manufacturing Company. I know that they used to work in a fabric mill, and it is right across the street. A drawing of the mill is found on the map:
So, I also searched for a picture of the mill online and found this via:
More information about the mill, via: "The Springville Manufacturing Company constructed a modern brick mill in 1886 at 155 West Main Street. The building was equipped with automatic sprinklers, elevators and electric lights. It features a five-story stair-and-bell tower with a slate-shingled pyramid crowned by a pair of finials." ..."the Hockanum Company, Springville Manufacturing Company, New England Company, and the Minterburn Company formed a holding company for the purposes of purchasing raw materials and distributing finished goods. The holding company, called The Hockanum Mills Company, constructed an addition to the Springville Mill offices at 155 West Main Street in 1909. This was among the last buildings constructed by Rockville's woolen textile manufacturers. In 1934, the Hockanum Mills Company sold all of its holdings to M.T. Stevens and Sons of North Andover, Massachusetts."