First, I started reading The Hunger Games. I've only finished a few chapters, so I can't yet tell you if I love it or hate it. But, I can tell you that I'm enjoying it much more than I did the first book of The Twilight Saga. This has no connection to whether Katniss is a real name, but I thought it was worth following up on.
Second, I've since looked into the number of names that have been derived from written works. There are tons. This just makes sense. Before there were telephones, television or internet, people communicated through writing - newspapers, poetry, letters and books. In addition to spreading ideas and information, written communication introduced and popularized names. While I'm not going to take back my declaration (because I'm stubborn and I wouldn't personally name my child Katniss), I will share a few details of my findings.
Jessica. The first documented use of the name Jessica was in William Shakespeare's The Merchant of Venice. Who knew? Bill Shakespeare also created the name Miranda in his work, The Tempest. The name Pamela was invented by Sir Philip Sidney in The Countess of Pembroke's Arcadia. Poet Jonathan Swift originated the name Vanessa for his 1713 poem "Cadenus and Vanessa".
There are also a handful of names were made popular, though not invented, by a writer. Wendy. You've heard of this name, yes? J.M. Barrie popularized the name Wendy in his little known book, Peter and Wendy (the story of Peter Pan). Charlotte Bronte popularized the name Shirley in her novel entitled Shirley. Suzanne Collins, author of The Hunger Games, didn't invent the word Katniss, but she will most certainly be responsible for popularizing it as a name.
Katniss is a plant.
Here is a guide on how to grow the katniss plant...
if that strikes your fancy.(image here)