The light novel series for 'Violet Evergarden' is a bit of an interesting case to track down. As far as I know, there are four main volumes. The author is Kana Akatsuki, and the illustrations are by Akiko Takase. The main story is contained in those four books. However, I recall there was also a side story collection released, which sometimes gets counted separately. So if you're just looking for the core narrative, you've got the four volumes to hunt for.
Finding them in English was a whole journey for me. The official translation from Yen Press only covers the first two novels, I believe. I ended up reading fan translations for volumes three and four online because I just had to know how it all ended. The ending in the novels is quite different from the anime adaptation, especially regarding Violet's ultimate fate and her relationship with the Major. It's a much more conclusive and, in some ways, a darker resolution.
Honestly, the light novels have a different feel. The prose is very detailed and introspective, diving deeper into Violet's internal monologue as she learns about emotions. The anime visuals are stunning, but the books let you sit with her confusion and gradual understanding in a way the show sometimes speeds through. If you loved the anime, the novels are absolutely worth seeking out, even if you have to piece together the translation sources.