Thank you for writing.
This is a difficult problem because of the walnut (it would help to know which kind of walnut).
https://extension.psu.edu/landscaping-and-gardening-around-walnuts-and-other-juglone-producing-plants

For ground covers, viola, squill, bluebells, sweet woodruff will all work and would well be mixed in with the grass for an attractive spring lawn.
https://www.gardeningchannel.com/juglone-tolerant-plants-grow-black-walnut/

https://nativeplantherald.prairienursery.com/2016/06/planting-under-black-walnut-trees/

https://www.prairienursery.com/plants-seeds/site-solutions/black-walnut-tolerant.html

Your best bet for grass would be fescues which can be obtained at most large garden stores. This is a robust lawn. Weed and rake well. Plant in spring or fall.
https://www.arboretum.umn.edu/UserFiles/File/2015%20Earth%20Day/Low%20maintenance%20lawns,%20arboretum%20final-sam%20bauer.pdf
https://www.twincities.com/2016/07/06/fescue-grass-mow-once-a-year-less-water-no-fertilizer/

Thank you for the very fast response.  I don’t know what kind of black walnut it is, but you sent a huge amount of information that will be very helpful in planning my spring plantings.  Thanks again!!

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