Those are extremely different schools. My gut is if you are even considering Williams that EA at Notre Dame is a bad idea just because I cannot imagine it is a fit. But something must have gotten these two schools to the top of your list. What is it you like about each one? Have you visited ND during a school year? Williams?
I did visit ND (we live in nearby state) and like it so much. I didn’t get chance touring Williams college due to the current covid restriction ( didn’t feel like flying) I will definitely go to graduate school so would like to have a decent undergraduate education.
I agree that these 2 schools are very, very different. It is hard to imagine the same student being equally happy at both. Just looking at undergrad enrollment, ND has 4 times as many students as Williams. In addition, ND has twice the number of Williams students as grad students. If you haven’t visited Williams, and you aren’t bothered by the size of ND, do not apply ED to Williams. I would worry it will feel claustrophobic once you actually see it.
Excellent advice from @helpingmom40. It may appear that it’s “easier” to get into Williams ED, but unless you are a recruited athlete or have some other strong hook, e.g., FGLI, legacy, etc., you’re still facing daunting odds in the ED pool. If you love ND, apply EA. You have nothing to lose. If you apply and are accepted by Williams RD, you can visit in the spring. Good luck.