Q.Emerald Green Arborvitae Dying?
I planted these 5 Emerald Green Arborvitae’s in my yard here in suburban Chicago back in June. They have been doing very good until the last two weeks. All of a sudden they look like they are dying? The one all the way on the right in the picture looks particularly bad.
Any advice?

No photo came through. My first guess would be water deficit (drought stress). If you think that may be a possibility, deep water the entire root zones right away, not just near the trunk, but all the soil surface under the foliage and more.
Excess water and root rot an also be an issue.
But if you believe that the plants have had appropriate irrigation, not too much or too little, then consider some of the other factors that could be related to the decline: Water pipe leak and root rot, gas line leak, herbicide overspray, gopher damage to roots, rodent damage to lower stems, pest and fungal disease issues:
The University of Illinois Extension may help with local information and even a site visit from an advisor.
https://ipm.illinois.edu/diseases/rpds/622.pdf
https://homeguides.sfgate.com/causes-emerald-green-arborvitae-turning-brown-37045.html
https://homeguides.sfgate.com/emerald-green-arborvitae-disease-44425.html