Here's where you can find that information:
* The copyright page: Look at the very first or very last page of the book. The copyright page will list the year of publication, along with other legal details.
* Online book retailers: Websites like Amazon, Barnes & Noble, or Goodreads will display the publication date for each book in their listings.
* Wikipedia: The Wikipedia page for each Harry Potter book will also list the publication date.
* Official Harry Potter website: The official website for the series might also have a page with publication dates for the books.
Let me know if you have any other questions about the Harry Potter series!