Markree Observatory was an astronomical observatory in County Sligo, Ireland.
In 1830, Col. Edward Joshua Cooper MP (1798–1863) eldest son of Edward Synge Cooper MP, and Ann, daughter of Henry Vansittart, Governor of Bengal, set up Markree Observatory on the grounds of Markree Castle."The Observatory of Mr Cooper of Markree Castle - undoubtedly the most richly furnished private observatory known - is worked with great activity by Mr Cooper himself and by his very able assistant, Mr Andrew Graham." (Royal Astronomical Society, 1851).
In 1878, Cooper’s assistant, Andrew Graham, discovered the asteroid 9 Metis with the Comet Seeker. Graham resigned his post at Markree in 1860, but continued his research at Cambridge Observatory until his retirement in 1905. E.J. Cooper died in 1863, but the observatory remained active until the death of Edward Henry Cooper MP in 1902.