The graph above shows how many newborns received the first name Henk since 1880. Henk was a popular name in the 1960s, but has been losing ground ever since. Currently I am one of 6892 men and boys who have Henk as their first given name. There are also 5658 men and (surprisingly) 55 women who have Henk as a second or later given name.
It seems from the graph that the name Henk was introduced in the 1910s. That is not the case: The name existed long before that, but people called Henk were officially registered as Hendrik (or sometimes Hendrikus). Here is the same graph for the name Hendrik:
Hendrik has always been a popular name, until the 1970s. It already started its decline in the 1960s, when the short form Henk became popular, and declined sharply since the 1970s, when traditional Dutch names made space for new, often foreign, names. Nowadays, many parents give their children two names: A modern name for daily use and a traditional name because of our custom of naming children after their grandparents. The next graph shows the popularity of Hendrik as a second (or later) name, As you see, the decline in this graph is much less pronounced.
Note, by the way, the peak in the mid 1940s in all graphs: This is caused by the post-war baby boom, the increased number of births in the years after the second world war.
The map below shows the name Hendrik is common everywhere except in the southeast, but especially in the northeast. The graph shows which part of the male population has Hendrik as first given name: More than 5% in large parts of the northeast, 1-2% in the densely populated west, and less than 0.5% in most of the southeast (but there Hendrikus is a common name).