Project Architect, Whidden and Lewis, Architects, Portland, OR, 1891; Partner, Ellicott and [Edgar M.] Lazarus, Architects, Portland, OR, 1892-1895;

Born in Philadelphia, PA, Ellicott's family lived on or near a farm in a large residence populated by servants. He lived in Portland, OR, between 1891-1895. He lived in Baltimore, MD, by 1920. In 1930, he and Anna lived at 714 Saint Paul Street, Baltimore. They owned their own house, valued approximately at $15,000; the family had enough money to afford to pay a live-in African-American servant, Laura Peters, (born c. 1875 in MD).

His father, William Miller Ellicott, Jr., was a "retired druggist" in Philadelphia, PA, in 1880; he had been born in MD. William III's mother, Nancy M. Ellis (born c. 1840 in PA) came from some wealth, her father Charles Ellis (born c. 1800 in PA), also a drug merchant, had a residence worth over $20,000 in 1870 and a household staff that included six servants. After her marriage, Nancy maintained a similarly-sized household which included (in 1880) her four children: Charles E. (born c. 1862 in PA), Mary M. (born c. 1866 in PA), Edith (born c. 1871 in PA) and Lydia (born c. 1872 in PA); her mother, Mary L. Ellis (born c. 1803 in NJ or PA, a "lady of leisure" according to the US Census) and sister, Deborah Ellis (born c. 1827 in PA); Annie L. English (born c. 1858 in PA), a governess; Martha Orr (born c. 1826 in Ireland), the cook; Catherine Flood (born c. 1859 in Ireland), a seamstress,; Mary Kilgas (born c. 1858 in PA) and Sarah Evans (born c. 1861 in PA), 2 servants; and a farm hand, Daniel Astley (born c. 1859 in PA).

He married Anna Campbell Ellicott (born c. in New Orleans, LA). Her father was raised in AL, her mother, MD.

Ellicott traveled a great deal during his life. In 1920, he and his wife, Anna, requested a US Passport for travel to Spain, Italy, France and Belgium. He and his wife were to leave New York, NY for Europe on 03/31/1920; they returned to New York, NY, via the Cunard liner R.M.S. Mauretania on 09/25/1920. He left 05/20/1922 for another six-month excursion to France, Belgium, Italy, England, India, China and Japan. At age 58, Ellicott was described as standing 5 feet 9 and 1/2 inches, having an oval face, high forehead, straight nose, blue eyes, round chin, thinning auburn hair and a fair complexion. He also sported a moustache. At some point, he had his appendix removed.