State income tax - where to file?

[RedCab]

My son attends college in Wisconsin.

I am a California resident. I claim him as a dependent.

During the summer he was supposed to work in Chicago, however due to Covid he worked remotely, from a combination of Wisconsin and California.

His employer withheld Wisconsin state taxes. I expect he is due a refund of WI taxes.

Do I need to file for him in California? (A quick pass thru turbotax and he owes < $100; none was withheld.)

Do I need to file in Wisconsin? (I want to, because I believe he will be due a refund of most of what was withheld)

Guidance appreciated!!

[MaryK4]

He would need to file in his resident state.  You do not provide enough information to determine this decisively, but see  Guidelines for Determining Resident Status (FTB Publication 1031).  He is most likely still a California resident so he would have to file a California income tax return.  

Because he worked in Wisconsin, he would have to file a nonresident WI tax return.  Because teleworkers residing in California working for a company in another state due to COVID-19 will not be taxed in California, all of his income would be taxed by Wisconsin.  

See also How do you file taxes for 2 different states? - TurboTax.