William married Agnes M Hardenbergh on 5 Jun 1888 in Minneapolis, Hennepin County, Minnesota, USA. Agnes (daughter of Charles Morgan Hardenbergh and Mary Lee) was born on 22 Dec 1863 in Chicago, Cook County, Illinois, USA; died on 8 Jan 1963 in Hennepin County, Minnesota, USA. [Group Sheet] [Family Chart]

1. William Penrose Hallowell, III was born on 14 Apr 1891 in Minneapolis, Hennepin County, Minnesota, USA; died in 1913 in Minneapolis, Hennepin County, Minnesota, USA.