What is the only U.S. state without a rectangular flag?

Ohio is the only U.S. state with a non-rectangular flag. Adopted in 1902, its distinctive swallowtail design, known as a burgee, resembles the pennants traditionally flown by cavalry units and sailing vessels. The flag's red, white, and blue colors reflect the national flag, while its 17 stars represent Ohio's admission as the 17th state to join the Union. The large white circle with a red center forms the letter "O" for Ohio and also symbolizes the state's famous nickname, the Buckeye State, named after its native trees found throughout the state.