There are only about 14 blue monkeys in all of North America's zoos, and that includes at least 8 at Omaha's Henry Doorly Zoo.
The blue monkey is recognized as special by the zoo, they have a picture of one on the cover of their map!
@Jonas broos The photo shows the entire exhibit and as far as I know there is still zero access to an outdoor enclosure. The building is more than a hundred years old and a historic landmark for Kansas City Zoo, although I'm not sure if there are still Blue Monkeys inside as this photo is now a decade old.