Shuck the corn, then place the ears in a large pot with the potatoes. Add water and 1 tablespoon salt to cover by 2 inches. Bring water to a boiling. Boil, covered, for 2 to 4 minutes, until corn is tender. Remove corn. Continue to boil the potatoes 15 to 20 minutes until very tender.
While the potatoes cook, finely chop the onion. In a large bowl combine chopped onion, vinegar, salt, and the 1/2 teaspoon pepper. Cut the kernels from ears of corn, then add onion to bowl.
When potatoes are very tender, drain in a colander. Cool enough to handle. Place potatoes on a board, then press with hands or potato masher to break up. Add potatoes to the onion and corn. Add the oil; gently stir to combine. Let salad come to room temperature, then add herbs and season with salt and pepper to taste. If desired, cover and refrigerate up to 24 hours. Let stand at room temperature for at least 1 hour before serving. If needed, toss with additional olive oil and vinegar before serving.