UIUC has a CS major and 9 or more CS+X majors (econ, math, anthropoly, geology, etc).
These are the approximate acceptances I managed to find
Computer Science (in Grainger College of Engineering): Acceptance rate - 7%
Computer Science + (all the CS + majors above): Acceptance rate: 10-20%
does any parent/student have an idea on the intake for some of these CS+X variations? If the intake is 30 seats, the higher acceptance doesn’t matter 
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Enrollment by major by class is here:
The numbers that @Mwfan1921 provided look to be very interesting and useful, and do seem to answer your question.
However, I have another way to look at this. Computers are used in a very wide range of applications. A lot of what a software engineer does is to take something that either humans have been doing or that humans wish that they could have been doing, and get computers to do it for us. Quite a bit of this involves a lot of data. Thus in physics there is a lot of use of computers to align the beam on a cyclotron or to analyze the piles of data that results. In astronomy computers can aim telescopes and analyze the piles of data that results. In acoustics computers (and quite a bit of math) can be used to ensure that every seat in a concert hall has good sound quality. This trend continues across a huge range of different engineering and scientific fields.
To me the combination of computer skills plus knowledge in a particular area is a combination that can result in an interesting career.
In my case I was a math major. However, I also took a lot of computer science courses. The total course load that I took came out to be very similar to something like what MIT now calls “Mathematics with Computer Science (course 18C)” (this specific major was not available when I was there, but the courses were mostly available). This is a combination that got me jobs that were interesting, because I got to both look deeply at whatever math was needed and then program the computer to do it. A couple of times for example we were using canned software programs to analyze results, got results that just looked way wrong, and someone (which meant the math guy, which meant me) had to look closely at what math the software was using, and figure out why this did not fit the problem we were trying to solve. To me this is fun stuff (and they pay you).
Which leads to the question: Which combination would be “fun stuff” for you?
I think that you should apply for the major, whether a combined major or not, that you want. Then see where you get in and pick from among your affordable acceptances.
100% agree!
And OP, please not that these acceptance rates are usually lower for OOS and international students than for Illinois residents. Not sure where you’re applying from.
thanks @Momofthree24 and @DadTwoGirls
yes, i’m oos so very low chance 
this is the data i see for cs and physics, so 3 were enrolled as freshman and maybe 1 for oos
| Computer Science and Physics | 3 | 21 | 32 | 17 |
|---|
And the number increases for sophomore, junior, senior - those are then transfers or major changes ?
great advice , thanks
Both, publics like UIUC have articulation agreement with state community colleges. These students have transfer priority. Also, some number of students can come from DES (students who enter as undeclared freshman, regular CS major is not open to these students.) Others can go thru the ICT process (again, no CS ICTs.)