I took a look at the population age 45 to 64 in ND counties because it is an age group whose retirement is most likely to be hurt by adverse economic shocks in the near future.
A different age group in ND
North Dakota Age Breakdown
For those interested in a little more detail here is a nice little graph for you:
Annual Estimates of the Resident Population for Selected Age Groups by Sex for ND
Source: U.S. Census Bureau, Population Division; Release Date: June 2015