(covers information from several alternate timelines)
The Netherlands was a country on Earth located on the continent of Europe. The people of the Netherlands were known as the Dutch. The Netherlands flag was three horizontal bands of red, white, and blue. (ENT: "First Flight") Its neighbor countries at times have been Germany, Belgium, France and across the channel Old Britain.
Important people from the Netherlands were 17th century philosopher Benedict de Spinoza who wrote The Ethics, (TOS: "Where No Man Has Gone Before") and 19th century painter Vincent van Gogh, (TNG: "The Most Toys"; DS9: "Second Sight") and painter Johannes Vermeer who made paintings like The Concert. (VOY: "The Killing Game")
In a by the Borg created alternate timeline, a large area of the Netherlands was flooded in April 2063, as was witnessed by the crew of the USS Enterprise-E when they flew over the country. (Star Trek: First Contact)
In another alternate timeline, this time created by Vosk and the Na'kuhl, Vladimir Lenin had been assassinated in 1916 and Russia had never become communist. Adolf Hitler therefore "quickly took England", being able to keep his focus on the West after the successful occupation of France, Belgium and the Netherlands. (ENT: "Storm Front, Part II")