The flag of Ohio is one of the most unique of all the states in the USA. It uses familiar symbolism that is common throughout most of the flags of the states - as well as having a design similar to the flag of the USA. What makes this flag different is that it deviates from the standard rectangle design of US flags - and in fact is the only US state flag that is not rectangular. It is also not a triangle. It is similar to the cavalry guidon flag used by Union forces in the American Civil War.
The Ohio burgee is the official name of the swallowtail shape of the flag. The left side is flat, and the right side leads into a concave triangle, being less wide from top to bottom than the left side, because of an angle slightly less than 90 degrees on the top and bottom leading into the end. This design can be seen here.
On the left side is a large, blue triangle with a circle in the centre and several stars. The blue triangle represents the hills and valleys of Ohio. The circle, red on the inside and white on the outside, represents several things. They are - the Northwest Territory, the 'O' at the beginning of the name of the state, and the prominence of buckeyes in the state, hence Ohio's nickname of the 'Buckeye State.' Near the base of the triangle are 13 white stars, representing the 13 original states in the USA. At the right peak of the triangle are four white stars, which, when added to the 13 other stars, represent that it was the 17th state added to the Union, as it attained statehood on 1 March, 1803.
There are five red and white stripes on the right side of the flag. The middle one is red, with two white stripes in between the outside red stripes. The border red stripes are angled to be parallel to the edge of the flag, while the centre red stripe is perpendicular to the left edge. The sides of either white stripe touching the centre red stripe share the angle, and the sides of either white stripe touching the outer red stripes share the angle, making it so that the two sides of the white stripes are not parallel with each other. These stripes represent the roads and the waterways (specifically canals - two of the most famous canals in Ohio are the Erie and Miami).
The design was created by designer and architect John Eisenmann of Cleveland. It was adopted by the state legislature on 9 May, 1902. On the 100th anniversary of its adoption in 2002, the legislature created an optional end to the US pledge of allegiance for Ohioans (in the presence of the Ohio Flag), 'I salute the flag of the state of Ohio and pledge to the Buckeye State respect and loyalty.'