I don't live in Iowa, but I took a quick look at the Radioreference database and it tells me that what you were told appears to be true. There appears to be two statewide radio systems in your area, both p25 phase II digital. The state patrol is on the ISICS system, and has some encrypted tac channels but I think most dispatch stuff is in the clear:
Then your local towns and county stuff is on the SARA Network. Most of the law stuff for Linn and Johnson is encrypted, so no scanner can receive those. Linn fire is in the clear, but Johnson fire is encrypted.
So with a p25 phase II scanner you could monitor ISP and some fire. Both p25 systems employ simulcast in your area, so you would get the best results with one of the newer Uniden scanners, the SDS100 or SDS200, which are designed to work well with simulcast.
You might want to ask a moderator to move this thread to the Iowa forum where folks with local knowledge might be able to give you more information.
Hope that helps.