1936 – Solo exhibition in Gallery ‘De Ronde Brug’, Amsterdam
1940 – Exhibition with ‘De Onafhankelijken’ (The Independants) in the Stedelijk Museum, Amsterdam
1945 – Exhibition “Kunst In Vrijheid” (Art In Freedom) in the Amsterdam Rijksmuseum
1948 – Group exhibitions in Laren and Amersfoort
1949 – Koert’s drawing of St. Paul’s Cathedral in London acquired by Rijks Prentenkabinet of the Amsterdam Rijksmuseum
1950 – Group exhibition of Contemporary Painters at the Wildenstein Gallery, London
1952 – The 123rd exhibition of the Royal Hibernian Academy of Arts at the National College of Art, Dublin
1954 – Summer Exhibition of the Royal Academy, London
1954 – Koert gives a talk and show of his work at the United Arts Club, Dublin
1955 – Summer Exhibition at the Royal Academy, London
1955 – Exhibition at Koert’s mother Nanetha’s home ‘Delvere’, Peaks Hill, Purley, Surrey, England
1955 – Second exhibition at the Wildenstein Gallery, London
1956 – Solo exhibition at ‘Little Theatre’, Brown Thomas, Dublin
1967 – Dutch Contemporary Art Exhibition at Municipal Gallery, Dublin
1968 – Irish/Dutch exhibition at Municipal Gallery, Dublin
1969 – Solo exhibition at Kunsthandel Martinus Liernur, The Hague, the Netherlands
1970 – Group exhibition at Killakee Art Gallery, Rathfarnham, County Dublin
1971 – Solo exhibition in Mullingar, County Westmeath
1972 – Solo exhibition at Molesworth Gallery, Dublin
1973 – Solo exhibition at Graphis Gallery, Dublin
1975 – Dutch Exhibition at Bank of Ireland, Dublin
1977 – Group exhibition during Dun Laoghaire Arts Week, County Dublin
1979 – Retrospective exhibition at Lad Lane Gallery, Dublin
1980 – Group exhibition during Dun Laoghaire Arts Week, County Dublin
1980 – Koert receives an award from Royal trust Company (Ireland) for ‘Croagh Patrick in the Snow’
1980 – Solo exhibition at home, Ballylusk, Ashford, County Wicklow
1982 – Group exhibition in aid of Gorta at Bank of Ireland, Dublin
1983 – Exhibition of work by staff members of the College of Marketing and Design at Bank of Ireland, Dublin