Is it harder to get into schools like Michigan, Illinois, Purdue for undergrad or grad?

Just curious because I am applying to CS grad schools towards those caliber schools and would like advice.

That is difficult to say, because the standards used are very different. Grad admissions see a higher caliber of applicant and are focused on more difficult-to-quantify research potential than in simple matters of GPA and test scores. I believe that these schools tend to see significantly lower admissions rate for grad than they do for undergrad, but I cannot say that for certain.

Regardless, you will not be applying to both at the same time, so what really matters is what you can do to make yourself a desirable candidate for admission at your present level.

Purdue’s acceptance rate for grad school is significantly less than undergrad. Not sure about the others on your list.

Undergrad admissions and grad admissions are totally different animals. Also, the very same person will be totally different animals when (s)he applies for undergrad and when (s)he applies for grad.

For undergrad, my D applied to 10 schools and got 2 accepted, 2 wait-listed, and 6 rejected.

For PhD 3 years later, she applied to 10 same schools and got 5 accepted and 5 rejected.

I don’t think anyone can say grad admissions is easier than undergrad admissions.