The walk leaves Paris on Saturday morning, camps two nights in fields along the way, and ends with Mass at Chartres Cathedral on Pentecost Monday. Pilgrims walk in chapters of roughly 20 to 60 people, each named for a saint and usually built around a parish, school, or university; foreign chapters are grouped together and marked by black ribbons, and English-speaking chapters from the United States, Britain, and Ireland walk every year. The organizers list distances by category: adults 18 and over, about 100 km; teenagers 13 to 17, 75 km; families with children 6 to 12, 50 km; and Guardian Angels, who pray and support without walking.
Logistics are handled by the organization: trucks carry luggage between bivouacs, color-coded with black for foreigners, large tents are provided, and the kitchen serves breakfast and evening soup, with bread and water on the route; the Order of Malta runs the medical posts and shuttle buses pick up those who cannot continue. You bring a sleeping bag, mat, broken-in hiking boots, rain gear, and a day pack; the ground is often muddy and rocky.
To join from the United States, register on nd-chretiente.com once registration opens on Palm Sunday, choosing a foreign chapter or contacting a chapter leader, who manages foreign registrations directly. Fees are not published on the English pages read for this answer; confirm them in the registration form. The Mass at Chartres and the pilgrimage's liturgy are in the traditional Latin form. The existing page on visiting Chartres Cathedral from Paris covers the cathedral itself.