Types of districts
Most of the districts are rural districts (Landkreise). There are 295 Landkreise.
Cities with more than 100,000 inhabitants (and smaller towns in some states) are not usually part of a district, but do the work of a district themselves. These are known as urban districts (Kreisfreie Städte or Stadtkreise) The equivalent in the United Kingdom is a unitary authority, they do the work of a town and a county. There are 107 of these Kreisfreie Städte.
This makes a total of 402 districts.
In North Rhine-Westphalia, there are some cities with more than 100,000 inhabitants which are not urban districts, for example Iserlohn, Recklinghausen, Siegen, Paderborn, Bergisch Gladbach, Witten and Neuss. These cities belong to a district, but still do so the districts jobs themselves, as though they were independent.