Author Rick Riordan, whose book for young readers is No. 1 on this Sunday’s Wall Street Journal best-seller list, is expected to draw some 900 readers or more tonight at the St. Louis County Library. Note: the Journal’s best-seller list doesn’t relegate children’s books to their own list - it includes all trade books. His book is also No. 4 on amazon.com, so he’s obviously popular even if it might not be as well known as J.K. Rowling or Stephenie Meyer.

His new book, “The Last Olympian,” is the last in his series featuring Percy Jackson and the Olympians. It’s geared toward readers 9 and up, although the hero of the fantasy series approaching 16.

Carrie Robb of the county library headquarters says they are expecting hundreds of Riordan’s fans. But if more than 900 come, some will have to wait outside for the book signing. The event starts at 7 p.m. at 1640 North Lindbergh Boulevard. The only variable at this hour seems to be possible bad weather, which might keep some people at home, Robb says.