The Shirebourn is a lesser river of the Shire's Eastfarthing. Its source was in the uplands of the Green Hill Country, from where it flowed south and then southeast, where it matched the boundary with the Southfarthing. At Willowbottom, it met the Thistle Brook, and then flowed eastwards.
The Shirebourn flowed into the Brandywine beneath Deephallow, and at its mouth formed the boggy region known as the Overbourn Marshes, opposite the southern end of the High Hay. Its outflow was the Mithe.
Shirebourn means "Bright-stream". However, in most translations, it is translated "River of the Shire" instead.