William Cranch (July 17, 1769 – September 1, 1855) was a United States circuit judge and chief judge of the United States Circuit Court of the District of Columbia. A staunch Federalist and nephew of First Lady Abigail Adams, Cranch moved his legal practice from Massachusetts to the new national capital, where he became one of three city land commissioners for Washington, D.C., and during his judicial service also was the 2nd Reporter of Decisions of the Supreme Court of the United States and a Professor of law at Columbian College (which later became George Washington University).

Cranch was born on July 17, 1769, in Weymouth, Massachusetts to Mary (Smith), a sister of First Lady Abigail Adams (Smith), and Richard Cranch, who had emigrated from Devonshire when he was twenty years old. His father, although educated as a watchmaker, became the town's postmaster and an ardent patriot during the American Revolutionary War. The elder Cranch then studied law and won election to the Massachusetts legislature (serving in both houses), then served many years as a judge of the court of common pleas, as well as wrote a religious book and received two honorary degrees from Harvard.

Cranch was born at the home of his maternal grandparents, Rev. William Smith and Elizabeth Quincy of the Quincy political family, about 12 miles south of Boston, since his mother retreated there from a smallpox outbreak in Boston. He was the only son of Richard and Mary, who both died within a day of each other, on October 16, 1811. Cranch received his first schooling from his mother, who also instructed him in Latin and Algebra. Then he prepared for Harvard College under the guidance of his uncle, Rev. William Shaw of Haverill, Massachusetts.

Cranch attended Harvard University with his cousin, John Quincy Adams, whose later-published diary mentions him. Cranch graduated in 1787, then read law with Thomas Dawes, a relative by marriage and judge of the Massachusetts Supreme Judicial Court.

Admitted to practice in the Massachusetts Court of Common Pleas in July 1790 and before the Supreme Judicial Court the following year, and New Hampshire courts not long after, Cranch began a private legal practice in Braintree, Massachusetts. He continued private practice in Haverhill, Massachusetts from 1790 to 1791. His first judicial position, as common for young lawyers of the time, was justice of the peace for Essex County, Massachusetts.

Following Congress's decision to move the capital to a new federal city in 1790, the 25-year-old Cranch moved to the area ceded by Maryland and Virginia that would eventually become Washington, D.C. Cranch was a land agent for the real estate firm of Morris, Greanleaf & Nicholson. He spent winter poring over accounts provided by his brother-in-law James Greenleaf (who was initially his sole client). Greenleaf had considerable property in the new capital city, and also speculated in Georgia land, but his $800,000 profit proved only on paper because a subsequent Georgia legislature voided the sale because the previous legislature had been bribed. Cranch later considered the experience, "learning the tricks of the world and the deceitfulness of accounts", perhaps in part because Greenleaf did not pay him money, but instead let Cranch use a 2,200 acre estate across the Eastern Branch of the Potomac River, where Cranch showed friends "the labor of my hands--my beautiful orchard, my peas, my melons, my grapes, my wheat and rye, my cabbage and lettuce" as well as various varieties of apples, pears, peaches, cherries and grapes, complaining only that only a single small rain shower had fallen in 57 days.

Before President John Adams moved to the new capital city, Greenleaf paid the new city's commissioners $120,00 and also spent more than $140,000 on a map, buildings and bridges, but found he had done so on the worthless promises of his partners Morris and Nicholson. Moreover, a man Greanleaf thought owed him money, William Duncanson, sued him and whipped Cranch for his legal actions on Greenleaf's behalf (but Cranch heeded Abigail's advice to trust in the law and "holy religion" rather than retaliate in a duel, as had Greenleaf). Greenleaf would go bankrupt and spent time in debtor's prison, as would another of Cranch's speculator clients, Robert Morris, but Cranch himself avoided debtor's prison for debts he had incurred on Morris' behalf when friends saved his property at the sheriff's sale (Cranch also took in boarders to meet expenses and eventually repaid all his creditors). Cranch's fledgling legal practices also had highs (such as winning a verdict in Annapolis from his client and creditor Law) and by the turn of the century, Cranch had filed over a thousand lawsuits in Maryland courts. Nonetheless, the pecuniary troubles nearly caused Cranch to move back to Massachusetts, but he reconsidered after one of John Adams' final acts as President.

In the waning days of his presidency, President Adams appointed Cranch one of the new Federal City's commissioners (the local government). Cranch replaced Gustavus Scott and served for less than two months in 1801, trying to extricate the board from its lack of cash and general financial plight, while also continuing his vigorous private legal practice. On February 27, 1801, Congress passed the District of Columbia Organic Act of 1801, which among other things established the court system and Cranch became one of the city's first judges, leaving his role as commissioner. The court initially opened in Alexandria, Virginia (then part of the federal city) and after a courthouse was built in Washington, would alternate sessions between the locations. A lack of housing in the new city meant that at times Cranch resided in Alexandria, Virginia. In 1825, Cranch moved his residence across the Potomac River, to Delaware Avenue.