John Dearness was born in Hamilton, Ontario on May 13, 1852, the oldest child of John and Jane (née Linklater) Dearness. The family moved to the Granton, Ontario area in 1856. Dearness graduated from the Toronto Normal School in 1871 and, at the age of 19, started teaching at School Section #1 (Coursey School) in Biddulph Township. Over the next four years, Dearness would become principal of Lucan School and also teach at elementary and secondary schools in Strathroy.
In 1874, Dearness was appointed inspector of public schools for East Middlesex County. He would travel throughout the area inspecting schools for the next 25 years.
Dearness married Harriet Emma Wilkinson (b. 4 July 1861), one of his former students, on June 20, 1881. Together, the John and Emma had three children:
Jean M. Dearness Tuke (25 May 1882 - 1967)
Margaret E. Dearness Tamblyn (23 Nov. 1883 - 1976)
Walter Dearness (5 Nov. 1886 - 9 Mar. 1957)
In 1888, Dearness began teaching biology courses at the University of Western Ontario and was appointed chair of the medical faculty. He received his own Bachelor of Arts degree in 1902, and Master of Arts degree two years later. Dearness was the first person to scientifically describe the hawthorn mealybug (Phenacoccus Dearnessi) in 1900, and a new species of scale insect (Aspidiotus Dearnessi) in 1897.
When the London Normal School was opened in 1900, Dearness accepted the position vice principal, serving in this capacity until 1918, when he assumed the role of principal. Between 1911 and 1915, he also taught summer school nature courses at the Ontario Agricultural College. Dearness retired from teaching in 1922, at the age of 70.
Dearness served as president of various associations at one time or another including:
London and Middlesex Historical Society
Ontario Historical Society
Mycological Society of America
Entomological Society of Ontario
He also served as secretary/treasurer of the Spelling Reform section of the Ontario Educational Association, and was a member of the Simplified Spelling Society.
John Dearness was awarded an Honorary Doctor of Laws degree from The University of Western Ontario in 1926, the King's Jubilee Medal in 1935, and made a Fellow of the Royal Society of Canada in 1936. Active in his writing and scientific pursuits until his 100th year, Dearness was a well known figure in London society. John Dearness died on December 6, 1954 at the age of 102. The Dr. John Dearness Home for Elder Citizens (now The Dearness Home), opened in 1952, and John Dearness Public School, built in 1967, were named in his honour.