There are lots of swallows in Utah. On the various trips I took last week I saw Tree, Cliff, Barn, Violet-green and Northern Rough-winged. I saw my fair share of their nests as well. Swallows seem to have adapted very nicely to the structures that humankind has created, so you will frequently find their nests under bridges and on the sides of buildings.
Within the Bear River Migratory Bird Refuge, the swallow populations were immense. I saw very large colonies of both Cliff Swallows and Barn Swallows. At the refuge visitor center, for example, you can watch Cliff Swallows tend to their mud nests and the chicks within just by parking your car and walking a few yards to the front door. Stop right outside the front door and look up at the building to your right. They are impossible to miss.