There is no one book I can point to and say “that’s the first book I found and read on my own”. My parents always encouraged reading and read a lot around me. I had free access to the school library and went to the city library every few months. I know that I read a lot more than most of the kids in my homeroom, and that it was frustrating that no one ever wanted to talk about books.
I can point to several books and series that I know I found on my own, probably starting around third grade, and then continuing on.
Encyclopedia Brown - loved at the time, but was only occasionally able to figure out the mystery. Every now and then, I’d come across one that irritated the hell out of me (Sally solves the case Encyclopedia can’t, because she realized the bank robber was dressed as a woman when he sat on the wrong side of the restaurant table? WTF?). Looking back, they were age appropriate with strong characterization for that type of writing, but there’s really nothing to bring me back to them. (There’s also another similar series, only the main character is an inventor, and his little sister has an upturned nose, freckles, and is named Daphne. Anyone recognize it?)
A Wrinkle in Time - I’m with Skald. The Murrays felt like long-lost family, and I empathized with Meg the way I never had with another protagonist. I think I must have read the cover off the library copy, and then I discovered that Madeleine L’Engle had written many more books. I started with the Murray family books, found her non-fantastical juvlit, and worked my way into A House Like a Lotus and The Arm of the Starfish when I was in high school. When I went back and re-read her collection in my early thirties, I was amazed at just how much of her worldview I’d absorbed. Everything from the numinence of good in everything from the subcellular to the interstellar scale to the music mentioned to the ordinary, everyday hassles of family and school. I still love her.
I also read a lot of Apple paperbacks from Scholastic Press. It seems to me that there were a lot more one-offs under that imprimatur than now. Everything offered currently is a series and usually connected to a tv show. One that sticks out is The Girl With the Silver Eyes, which I’m astonished to find is still in print and available on Amazon.
Though I didn’t know it at the time, The Girl Who Owned a City was the first post-apocalyptic story I ever read, and I think it primed my tastes for a lifetime more. I didn’t notice it as a kid, but when I went back and read it as an adult, the paean to Ayn Rand is painfully obvious and not very well thought out. There’s a mention that Lisa finds a book in the library that explained how people and cities all worked and gave her the answers she needs to keep her band of survivors together. I wondered what it was when I was a kid. When I got a bit older, I figured it had to be Plato’s The Cave or some other similar philosophical work.
I know I also read Doctor Who novelettes, D’Auliere’s Greek and Norse mythology, and an indiscriminate metric ton of everything else. My other main source for fiction was comic books, and that started with X-Men #172, which is a wonderful place to start.