Knockboy, Mountain summit in County Cork, Ireland

Knockboy (Irish: An Cnoc Buí, "yellow mountain") is a 706-metre mountain on the border between counties Cork and Kerry. It is the highest peak of the Shehy Mountains and the highest mountain in County Cork, with its summit shared with County Kerry. It is the 104th highest peak in Ireland.

The mountain formed from sandstone deposits that were lifted during tectonic movements in the Devonian period. Glacial erosion during the last ice age then shaped the ridge and surrounding terrain into their current form.

The Irish name An Cnoc Buí means "yellow mountain", a reference to the colour of the ground cover on its slopes. The summit lies on the border between counties Cork and Kerry, so walkers can stand in two counties at once. The name appears in both Irish and English on maps of the area.

Multiple marked trails lead to the summit, with a surveyor's marker at the top to help with navigation. It is best to wear sturdy shoes and weather-resistant clothing, as conditions can change quickly on exposed ridges.

Knockboy is the 104th highest peak in Ireland, and its summit lies exactly on the border between County Cork and County Kerry. It is also the highest point of the Shehy Mountains, so the county top of Cork is shared with its neighbour.