Where at in central Illinois? I lived there my whole 47 years until I moved here to Florida 2 years ago...( I am 49.) Born in Peoria, moved to Glasford, then rural Lewistown then rural Ellisville, at the corner of No and Where.
Your bananas will certainly need to be kept warm. 40 will keep them alive but they won't grow until it's about 60 which is doable in a heated greenhouse there all but mid Dec thru mid Feb most years. It looks like you might have what some call truly tiny Cavendish, and while they will fruit, it's not easy.If it is a regular Dwarf Cavendish, which it may be, it will be easier to fruit, but you will need a bigger pot but be warned, dwarf is a relative term in bananas, it will still get 6-8 feet tall..Search here for truly tiny and learn the tricks to get fruit and ideas of other varieties you may be able to fruit before frost there like Veinte Cohol.
Here is your pic:
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Varieties I supposedly bought: Manzano, Cavendish, Blue Java, Sweetheart, and Gros Michel.
What it seems I actually have: Brazilian, Cavendish, Namwah, Dwarf Red, Gros Michel, Pisang Ceylon, Veinte Cohol and SH 3640, and American Goldfinger. FHIA 1, Paggi and FHIA 17... Always room for one more.