Markree Castle is a castle located in Collooney, County Sligo, Ireland. It is the ancestral seat of the Cooper family, partially moated by the River Unshin. Today it is a small family-run hotel.

Edward Joshua Cooper was an Irish landowner, politician and astronomer from Markree Castle in County Sligo. He sat in the House of Commons of the United Kingdom from 1830 to 1841 and from 1857 to 1859, but is best known for his astronomy, and as the creator of Markree Observatory.