William was one of three children: his brother Henry Trowbridge Dykman was born in 1856 and his sister Elizabeth was born in 1859.
William went to West Point Academy starting on 1 Sept 1871 and graduated in 1875. He graduated a Second Lietenant in the 22nd Infantry, and served until October of 1876. One of his last posts was at Fort Porter, in Buffalo NY. He is often listed in the Newspapers as Colonel William N Dykman, but that doesn't seem to be reflected in the military Records.
After William left the military he studied the law at Union University in NY and graduated in 1878. The law firm (Cullen and Dykman) he had with Edgar Cullen still exists today. William became a very well known lawyer in Brooklyn, taking many high-profile cases. William also headed the NY BAR Association for a time.
William married Isabelle Annan in June of 1885, daughter to Edward Annan. William and Belle had a son, Jackson Annan Dykman on July 11 1887. Jackson married Susan B Merrick on 3 Feb 1915 in New Orleans.
By 1897, William had applied for passports for himself, Belle, and Jackson so they could travel overseas. They travel to Southampton, England and to France by boat many times over the next 25 years, despite the fact Belle's niece was on the Titanic when it went down. William and Belle also were active in Horse club circles, attending shows and Polo games.
"White Acre", a large estate in Glen Cove, NY was established as William and Belle's home around 1912, designed by Harrie T. Lindeberg of Lindeberg's Domestic Architecture. It still stands today at 1 Meadowspring Rd on Long Island.
William Dykman died July 20 in 1937, and his wife Belle died March 31 1941.
Sources include:
New York and Ohio Newspapers
Johannes Dyckman of Fort Orange, Vol 2
The Trowbridge Genealogy
West Point Military Records
Federal Census Records
NY & UK Passenger Lists
US Passport Applications
Union University Record
Cemetery Records