I didn't know that Koko was still alive. She is still alive, she was born in 1971, and her statistics are impressive:

During the course of the study, Koko has advanced further with language than any other non-human. Koko has a working vocabulary of over 1000 signs. Koko understands approximately 2,000 words of spoken English. Koko initiates the majority of conversations with her human companions and typically constructs statements averaging three to six words. Koko has a tested IQ of between 70 and 95 on a human scale, where 100 is considered "normal." Michael, the male silverback gorilla who grew up with Koko, had a working vocabulary of over 600 signs.