A bit late

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@Stilldiscovering wrote:

Is it necessary to file a tax return on his behalf?

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Read through Publication 559 at the link below.

https://www.irs.gov/publications/p559#en_US_2021_publink100099488

You need to be concerned with filing responsibilities if your spouse was the personal representative or, in certain instances, if your spouse received property from the decedent.

Your spouse may also want to consult with a local tax professional and/or legal counsel.

OK. Thank you for the fast response, and insightful answer. 🙂

It's never too late to file.  If your father in law was entitled to a refund, it is too late to get it paid.

The more important questions are, was a return required at all (based on income and other factors), and who was the responsible person.  The responsible person to file a tax return might have been his child, but might not have been.  

To determine if a return was required at all, you can start by reviewing the 2017 instructions for form 1040, starting on page 4.

https://www.irs.gov/pub/irs-prior/p17--2017.pdf

If a return is required, you will have to see a tax professional who is willing to prepare a 2017 return, or do it by hand using the 2017 forms and instructions from the IRS web site.  Turbotax is not supported or available for purchase that far back. 

That would be the backward approach.

The threshold issue virtually always involves determining which party has a duty to file.

Much thanks for your detailed answer. I will reach out to an accountant. Thanks again:) 

Much thanks to all who answered.