A gemeente is a municipality, the lowest administrative unit. The Netherlands currently has 408 municipalities in 12 provinces. Over the last couple of decades, many municipalities merged. In 1812 there were 1,100.
Archives of municipalities can be found at a local archive; either a municipal archive specific for that municipality or a regional archive where the collections of several municipalities are kept.
For an overview of all the gemeentes, check the website Gemeentegeschiedenis (municipal history). Just type in the name of the former or current municipality for basic information like the dates it existed and a map.