Discover Plymouth, Indiana Plymouth is located at the heart of Marshall County, 100 miles north of Indianapolis and 85 miles east of Chicago. With a population of approximately 10, 000, Plymouth offers small town friendliness with the sophistication of a larger city. 120 North Michigan Street Plymouth, Indiana 46563 1-574-936-2323 Fax 1-574-936-6584 Email: plychamber@plychamber.org ...