Trigedasleng, the language spoken by the grounders, was created by David J. Peterson, the same person who created Dothraki, A language spoken in Game of Thrones (2011).
The series started filming before the first book was released. Accordingly, the two series (television and book) have almost nothing in common besides the names of a handful of characters and the basic premise of the very beginning of each.
Many of the young characters' names are taken from notable science-fiction writers: Clarke comes from Arthur C. Clarke, Wells comes from H.G. Wells, Octavia comes from Octavia Butler, Bellamy comes from Edward Bellamy. Many of the younger characters who aren't named after science-fiction authors are characters that were created for the series but who aren't in the source novel.
Since its release in 2014, "The 100" is the most watched show in its time slot on The CW.
Jason Rothenberg, the creator of the show, has stated that this show has always been Clarke and Bellamy's story and remains that way through the five seasons.