As the number of Instagram users continues to grow, an increasing number of public libraries are establishing and maintaining accounts on the Instagram platform. The objective of this study is to classify and analyze the content of Instagram posts from 14 public libraries that are actively engaged on the platform. A classification of post types, divided into seven large, 16 medium, and 76 small categories, was employed to analyze the content of posts on each library’s Instagram account from the account’s inception to the end of December 2023. The analysis revealed that library posts focused on a few items, including book recommendations, library introductions and news, and event announcements of literary and arts programs. Program event announcements and reviews, book recommendations and reading programs were found to be highly correlated with user engagement and teen reading programs. Based on these findings, it is recommended that future Instagram posts should be more user-centered and interactive, and that libraries should actively promote their events on Instagram and other social media platforms.