Charles F. Koss was born in Beloit.

The evidence

• “CHARLES F. KOSS, dealer in books, stationery, wall-paper, silver plated-ware and jewelry, Ea.st Bridge street; was born in Beloit, Rock Co., Wis., on Nov. 17, 1855 ; engaged in clerking from 1873 to 1876, when he entered into partnership with H. F.”

  1879-history-of-rock-county/18-bios-beloit.md, PDF p. 759

  Butterfield, C. W., et al. The History of Rock County, Wisconsin: its early settlement, growth, development, resources, etc. Chicago: Western Historical Company, 1879. Cornell University Library via the Internet Archive, archive.org/details/cu31924028871585.

  Grade A: Found on a page of one of our sources