The first library I remember is the Lakeland Public Library in Lakeland, Florida. This is what it looked like in the early 70s, a rather interesting and cool 1960s modernist building that was only a few years old at the time:
This is the equally modernist interior:
Unfortunately, the Lakeland Public Library no longer looks like this. It was renovated in the 80s in the style that shall be known as Post-Modernist Bland (if you're curious, you can view pictures at the Lakeland Public Library website, where I found these photos).
I revisited the library in 2007 and thought it looked different from how I had remembered (other than simply looking smaller, which was to be expected), but I wasn't sure exactly how it had looked in the 70s, my childhood memories being vague. So I was quite happy when I discovered these photos, not only to find that a photographic record of the old library exists, but also because I was glad to know that it looked so cool back then. Of course, it is also sad that they had to do away with something stylish in favor of something not so much, but you can't really blame the city of Lakeland entirely. They were just following the 80s trend (which has continued up to the present) of making buildings boring.