In a large pot, bring 8 cups of water to a boil over high heat. Add the Old Bay seasoning, garlic, and salt to the boiling water.
Add the halved potatoes to the pot and cook for about 10 minutes until they are tender.
Add the sliced sausage and corn pieces to the pot and cook for an additional 5 minutes.
Finally, add the shrimp to the pot and cook for 2-3 minutes, or until the shrimp turn pink and opaque.
Remove the pot from heat and carefully drain the contents into a large colander.
Squeeze the juice of the lemon halves over the shrimp boil and toss everything together.
Transfer the shrimp boil to a large serving platter or spread it out on a newspaper-covered table for a fun presentation. Garnish with chopped parsley before serving.