Killua Castle, Castle in County Westmeath, Ireland.

Killua Castle is a country house near Clonmellon, County Westmeath, built about 1780 by Sir Benjamin Chapman on the site of an earlier castle. Its grey-brown stone walls carry crenellated battlements, with a large round tower on the left and a square tower near the centre-right, both battlemented. Rows of rectangular and arched windows, some dark and empty, cross three storeys above a stretch of grass.

Killua Castle's lands were granted around 1667 to Benjamin Chapman, a captain in Cromwell's army, after being confiscated from the Knights Hospitallers of St John. The present house was built in 1780 by Sir Benjamin Chapman, 1st Baronet, after the original castle was demolished. His brother Thomas added a large round tower and several other towers in the early 1820s, completed the castellation and erected the Raleigh Obelisk. The house and remaining 1,200 acres were sold in 1949.

The castle connects to Ireland's potato cultivation history through a nearby obelisk marking where this crop was introduced. The memorial shows the place's role in the local agricultural story.

Killua Castle stands near Clonmellon in County Westmeath, with the Raleigh Obelisk about 200 to 300 metres from the house. The building was roofless and ivy-covered until its 2006 renovation, so the interior is not a furnished historic house. Approach from the Clonmellon side and look for the obelisk in the same visit.

The obelisk 200–300 m from the house was erected in 1810 by Sir Thomas Chapman to mark where Sir Walter Raleigh supposedly planted some of the first potatoes brought to Ireland. Its inscription now reads "Sir Walter G. Raleigh", but the "G" is thought to be later vandalism.