I'm not sure "trend" is the right word for Will County.
2016 - Trump: 43.6% - Clinton: 49.9%
2020 - Trump: 44.9% - Biden: 53.2%
Trump indeed outperformed his 2016 vote-share by 1.3 pts., but Biden increased Hillary's vote-share by 3.3 points. Also, roughly 41,000 more votes were cast in the county during the 2020 Prezi vs. 2016.
So if I had to guess, I'd say that high turnout was the catalyst for the increases in vote-share. But again, I wouldn't say that the county trended R -- at least to a statistically significant degree.
It still technically trended R since the nationwide 2016-2020 swing was D+2.4 while Will County swung D+2, but that's only an R trend of 0.4, so it is indeed statistically insignificant.
As for why Trump held up better here than the most of the other collar counties, it likely has to do with the fact that Will County has the largest WWC/lower-middle class element of all the Chicago suburban counties.
