Step 1: In a large mixing bowl, combine the softened cream cheese and sour cream. Beat them together using a rubber spatula or electric mixer on low speed until the mixture is completely smooth and creamy.
Step 2: Add the ranch seasoning mix to the cream cheese and sour cream mixture. Mix well until the seasoning is fully incorporated, scraping down the sides of the bowl.
Step 3: Gently fold in the well-drained Rotel diced tomatoes and green chilies, the drained sweet corn, and the shredded cheddar cheese. Mix until all ingredients are just combined.
Step 4: Taste the dip and adjust seasoning if necessary. You might want a little pinch of salt or pepper.
Step 5: Cover the bowl tightly with plastic wrap and refrigerate for at least 2 hours to allow the flavors to meld and the dip to firm up. For best results, chill for at least 4 hours, or even overnight.
Step 6: When ready to serve, give the dip a quick stir. Transfer it to a serving bowl and garnish with fresh chopped cilantro or green onions, if desired. Serve chilled with your favorite dippers.