I see a few jack rabbits every year, but way down from twenty years ago. I'd say, unscientifically, that the population is down 90%.
The ground squirrel population plummeted about 4 years ago. It went from bazillions (scientific word for lots of) to dozens. They are still around and hopefully will bounce back. They tend to go through phases of having the plague.
Cottontails seem to be holding steady, but nothing to yell about.
All said, the numbers of coyotes that I see has dropped as well. That's partly because of food supply and partly because they came through and shotgunned them from helicopters. Instead of driving across the street I have to go an hour or two to get into better coyote numbers.
SW Idaho.