He was baptized Cady Herrick, but his father thought it better to add an initial hyphened "D-" to the name to avoid class-room jokes, like calling the boy "Katie."

He graduated from the Albany Classical Institute, and then studied law in the office of Lyman Tremain and Rufus W. Peckham, Sr.

When Manning moved to Washington, D.C. to serve as U.S. Secretary of the Treasury in 1885, Herrick became the Democratic boss of Albany and continued in this role even after becoming a judge on the New York Supreme Court.

In 1891, he was elected to a fourteen-year term on the New York Supreme Court (3rd District), defeating Republican John T. McDonough.

In 1897, he overruled the Republican Secretary of State John Palmer's decision to certify the nomination of a candidate for Chief Judge by the "United Democracy".