William King was born on February 8, 1768, in Scarborough in the District of Maine.
He was the fourth of six children of merchant Richard King and Mary (Black) King, Richard's second wife.
William received his education at home except for one term at Phillips Academy in Andover, Massachusetts.
After working on the family farm and in various mills, William left Scarborough at age 19 to join his younger sister, Betsy, and her husband, Dr. Benjamin Porter, in Topsham, Maine.
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