The Charter Oak was important long before it served as a hiding place for Connecticut's Royal Charter. The tree was revered by Indians because of its great size, and was used by them as a Council Tree.

It became known as the "charter oak" due to an incident that is closely tied to Connecticut's Colonial history: On October 9, 1662, The General Court of Connecticut formally received a charter from King Charles II granting the colony with a degree of autonomy. With the succession of James II to the throne a quarter-century later, attempts to revoke the Charter began in earnest. Sir Edmund Andros, an agent of the throne, arrived in Hartford with armed forces to physically remove the document and in a candle-lit tavern on Main Street, opposing parties engaged in a debate over the issue, with the document on a table between them. When the candles were suddenly extinguished then relit, the document had vanished. Captain Joseph Wadsworth is credited with swiftly seizing the document, dashing to the Wyllys estate where the mighty oak stood and hiding the charter in a cavity of its trunk.

By the middle of the 19th century, the gnarled base of the tree measured over thirty-three feet in circumference. When the great tree fell during a violent wind storm (read the account below), the rings in its trunk were counted and the tree was deemed to be almost 1,000 years old.

Items of wood from the felled tree were fabricated, including an elaborate chair for the Lieutenant Governor in the State Senate Chamber, and a frame for the old Royal Charter in the State Library.

In addition, acorns from the great oak were planted in various locations around the city: one in Bushnell Park opposite 93 Elm Street; another in Bushnell Park in a location which no longer exists; one in the yard at 5 Collins Street; one in the yard at 82 Ann Street; and one at Armsmear on Wethersfield Avenue.

The tree was honored again on the Connecticut quarter, the last 50 State Quarters™ Program coin issued in 1999.