Casimir I of Kuyavia (Polish: Kazimierz I kujawski) (c. 1211 – 14 December 1267) was a Polish prince and a member of the House of Piast. He was Duke of Kujawy after 1233, ruler over Ląd from 1239-1261, ruler over Wyszogród after 1242, Duke of Sieradz from 1247-1261, Duke of Łęczyca after 1247, and Duke of Dobrzyń after 1248. He was the second son of Konrad I of Masovia and his wife Agafia of Rus. He was probably named after his grandfather, Casimir II the Just.