It looks like a calcaneus bone, which in humans and other primates is the heel bone of the foot. This one is from a left leg. In most non-human mammals it looks like it’s halfway up the hind leg, but serves the same purpose as the attachment point of the calf muscles (gastrocnemius and soleus), and its length acts as a lever to make the muscle action more powerful when flexing the foot towards the ground.
As a tentative ID from reseraching from my desk in the UK is white-tailed deer (Odocoileus virginianus), based mainly on its size and coming from Mississippi. The bone is a bit worn so some of the sharper and edges and points are missing, but the overall shape of the wide end looks like it matches the photos here https://www.boneid.net/search/?product_cat=wt_deer&pa_anatomic-elements=calcaneus&order=DESC. The length is about right too, if you imagine adding back on the points and edges that have been worn away.
For much more information on the calcaneus bone, see this ID of a cattle calcaneus Identification – cattle hock bone