IOI 2018 took place in Japan in September, 2018. More info is available on the official website.
Just happened IOI 2018 in Japan
The 5th International Olympiad in Informatics was held in Mendoza, Argentina in 1993. You can see four of the problems below, given as separate documents in pdf format for easy reading and printing.
Note that the grading model changed at IOI'94 and beyond.
Before IOI 1994, a human evaluator would sit behind the competitor's computer and do the testing manually (enter test data through the keyboard, check the output on the screen). Starting from IOI 1994, an automatic grading process is used, with test input defined in files.