As our boat wove among islands occupied by single stately homes sheltered by pines and leafless trees, a knowledgeable, droll guide told us all we wanted to know about the picturesque archipelago, from its ice age geological origins to its roguish Prohibition-era calling as a haven for liquor smugglers.

Standing on the sun-washed top deck, she pointed out the opulent estates built by the merchant princes Abraham Abraham and Nathan Straus and by George Pullman, designer of the railroad sleeping car, homes that rival the mansions of Newport. She also called attention to oddities like the footbridge from a Zavikon Island cottage to a satellite islet that allows you to cross from Canada into the United States without a passport.

Many islands are populated by turkey, otter, muskrat, deer and fox, and bald eagles can be seen atop the tallest pines. Some islands have granite cliffs; others are tiny, with one the size of a living room bearing a single juniper tree. (Only those spots that are above water year round and have at least one living tree qualify as islands.)

The largest, Wolfe Island in Canada, is 18 miles long, and has a year-round population of 1,400. Wellesley Island, the largest on the American side, has state parks that invite overnight campers, golf courses and its own lake, and it supports some of the five spans of the Thousand Island Bridge system, which connects Ontario to northern New York.

As the two-hour tour ended, we were told of one other distinction that George Boldt could boast of. According to one popular theory, he learned of fishermen who had patched together a salad dressing from the eclectic supplies of their campsite — mayonnaise, ketchup, Worcestershire sauce, sweet pickles and chopped onion. He liked it so much he served it at his elegant hotel, christening it Thousand Island dressing.

The region embraces several 19th-century mainland villages away from the hubbub that are worth visiting by car or bicycle. We were enchanted by Clayton, which has a series of uncommon shops, one selling several dozen flavors of olive oil and vinegar, another selling local cheeses and candy. The town has set up Adirondack chairs for quiet contemplation of the silent, majestic St. Lawrence. The Antique Boat Museum features 300 craft to savor and ride, including the region’s classic wooden runabouts. Not too far away is Cape Vincent, with an 1854 lighthouse that overlooks the passage from placid river to sometimes treacherous lake.