There are actually 101 frogs in the game if you include the frog behind the title at the very beginning and you will often finish the counter but still be missing an achievement. If this happens, check the only other guide for this game (the one by SadSensei) to find whichever frog you may be missing. That will get you the achievement!

Also, I'm only making this guide because I still need the Steam badge for making one, so give it a thumbs up! :)