I was recently asked the question of how I keep track of 100 library books. Since the answer is more than a sentence long, I thought I would post the answer here...
In 8 years I have lost ONE book... That book was found on my desk and the library refunded my fees.
We have specific locations for library books. We have a shelf upstairs for library books in our school room. Most books stay there. Often there are a couple books the kids are reading and those will be in their room by their bed. When they are done, they come back to the school room. I do have a shelf downstairs too for books that find their way downstairs.
Generally I only go to the library 2 days a week (yes 2) because those are the days I am around the corner from the library anyway. By confining my library trips to certain days, I always have my books due on the days I am going in.
Additionally, I LOVE LOVE LOVE Library Elf. Thankfully our library provides the service but I would subscribe if they didn't because it saves me time, effort, and money. Library Elf sends me an email when library books are due in a few days, due, or overdue. It shows me what is due on all cards (we sometimes have books due on up to 3 cards but I usually keep all books on 1 card) and I can also see what books are ready to pick up in one email. On my library days, I go through my library elf email. If there are books I want to renew, I go to the library website and renew otherwise I pluck them from the shelves and take them back.