From the ACLU page, a couple bullet points:

Roughly two-thirds of the United States’ population lives within the 100-mile zone—that is, within 100 miles of a U.S. land or coastal border. That’s about 200 million people.
Connecticut, Delaware, Florida, Hawaii, Maine, Massachusetts, New Hampshire, New Jersey, New York, Rhode Island and Vermont lie entirely or almost entirely within this area.
Nine of the ten largest U.S. metropolitan areas, as determined by the 2010 Census, also fall within this zone: New York City, Los Angeles, Chicago, Houston, Philadelphia, Phoenix, San Antonio, San Diego and San Jose.