In a large pot, add 6 cups of water, Old Bay seasoning, smashed garlic, and the halved lemons. Bring to a boil over high heat.
Once boiling, add the halved red potatoes and cook for about 10 minutes or until they are just tender.
Add the sliced smoked sausage to the pot and continue to boil for an additional 5 minutes.
Add the corn pieces to the pot and boil for another 5 minutes, allowing the corn to cook through.
Finally, add the shrimp to the pot and boil until they turn pink and are opaque, about 3-5 minutes.
Turn off the heat and use a strainer or slotted spoon to carefully remove the contents from the pot, draining excess liquid.
Arrange the shrimp, sausage, potatoes, and corn on a large serving platter. If desired, garnish with fresh parsley.
Serve immediately, with additional lemon halves on the side for squeezing over the meal.