The Monmouthshire flag (Welsh: Baner Sir Fynwy) is the flag of the historic county of Monmouth.

It was registered with the Flag Institute as the official flag of the county in 2011[1] although its origins date back to the 6th century.

The arms are those attributed by medieval heralds to King Inyr of the Welsh Kingdom of Gwent, from which Monmouthshire, once known as Wentset and Wentsland, descends.

The County Council of Monmouth were first granted the arms in 1948 and they have been incorporated into the arms of other bodies over the succeeding years.

The pantone colours for the flag are: Monmouthshire Council, which administers the principal area of Monmouthshire in the eastern part of the traditional county, uses a white banner charged with its coat of arms.