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 was more to the right of the national environment than last time, therefore it trended R. Which is weird, considering the other surrounding collar counties trended D:
Ah! Thank you, Woodbury. Was unaware that "trended" referred to a comparison vs. national environment.