Millard County, Utah is a great place to look for fossils, especially trilobites. There are several sites off old highway 50 as shown in the map below. The whole area is layered with fine shales that can be separated easily. The U Dig site is a fee area, but well worth the experience.
Lots of double-headed Agnostids are common.
The U Dig fossil site allows you to split stones and look for trilobites. They will loan you a chisel and bucket or you can bring your own. They allow you a certain amount of time to look and you can keep what you find. If it is a warm day, you will bake! The quarry areas are bowl-shaped and magnify the light. Take lots of water and a big hat.
The most common trilobites in the area are Elrathia sp.
If you launch out in the free areas, there are holes everywhere there is an outcrop of shale. There are many places where you can find lots of trilobites, it just takes longer to find a good spot and it may take more splitting, but part of the fun is finding your own.
There are many other spots in Millard County where you can find trilobites and other fossils. Consult the Millard County Rockhounding guide at https://millardcounty.com/activities/rockhounding/
for other areas of interest.
Generally, if you see that someone has been digging, that is a good sign that you could try your luck. Maybe they gave up, or got all that they wanted of what that hole had to offer. In one place where we were freelancing in the Amasa Basin, we found a hole that had a layer of trilobite parts...fascinating--build your own trilobite!
A lot of folks like to display their fossils on an easel or frame them to hang on the wall. Since the slate is easy to cut and shape you can also make a trilobite into a box top. A coat of clear acrylic will protect the fossil from scuffs or water damage.