Cornelis was not only extremely popular, but also extremely consistent in the Netherlands in the 1900s. It ranked at #3 in 1880, 1885, 1900, 1905, 1910, 1915, 1920, 1925, 1930, 1935, 1940, 1945, 1950, 1955, 1960, and 1965. In 1970 it dropped down to #6, and was out of the top 10 (however barely, at #11) in 1975.
Cornelis is used in Sweden too. A very famous and popular singer/songwriter in Sweden was named Cornelis Vreeswijk (nickname Kees). He was originally from the Netherlands.