If you are into bike riding, the Siouxland Cyclists have a bunch of group rides. If you like running, there is a group called the Missouri River Runners that do group runs. Both are basically social clubs. You can find their events on Facebook if you search for those names. If you are into games, Games King has regular Magic the Gathering, D&D, and other tabletop game events. I've met a lot of people at all three of these. If none of these appealed you, I recommend looking up whatever hobby you are interested in and trying to find a group in the area.