Island Park's 33-Mile Main Street: America's Longest
Island Park History · 8 min read · April 2026
The Town with America's Longest Main Street
If you've ever driven US-20 through Island Park, Idaho, you may have noticed something peculiar: the "town" never seems to end. That's because Island Park stretches an astonishing 33 miles along a single road — making it home to what locals proudly call "the longest main street in America."
But Island Park isn't a sprawling metropolis. Its population hovers around 300 year-round residents. The city limits are roughly 500 feet wide on each side of US-20, creating a corridor-shaped town that's 33 miles long but barely a quarter-mile wide.
How It Happened: The 1947 Incorporation
In 1947, the scattered communities along US-20 between Ashton and West Yellowstone decided to incorporate as a single city. The area included several small settlements — Mack's Inn, Last Chance, Pond's Lodge, and others — that had historically operated independently.
The residents drew their city boundaries in the most creative way possible: a narrow strip roughly 500 feet on either side of US-20, stretching from the southern boundary near Ashton all the way north to the Montana border near West Yellowstone.
The Liquor License Theory
The most popular explanation for Island Park's unusual shape involves Idaho's liquor laws. In the 1940s, Idaho required that a community have a minimum population to qualify for a liquor license. The individual settlements were each too small to meet the threshold on their own.
By incorporating all the settlements into one continuous city, the combined population exceeded the minimum requirement. The narrow corridor shape ensured every lodge, restaurant, and resort along the highway fell within city limits — and could legally serve alcohol to the tourists and fishermen.
Whether the liquor license was the primary motivation or simply a convenient benefit is debated among local historians. What's not debated is that the incorporation gave the scattered communities a unified voice and yes — the ability to serve beer and cocktails to thirsty anglers after a long day on the Henry's Fork.
What Is the Main Street?
Island Park's "main street" is US Highway 20, which runs north-south through the entire length of the city. It's the only through road, serving as commercial corridor, residential access, and scenic highway all in one.
Driving it, you'll pass through towering lodgepole pine forests, open meadows where moose and elk graze, the shores of Henry's Lake, and the banks of the legendary Henry's Fork. Speed limits fluctuate between 35 and 55 mph, and enforcement is famously strict.
Landmarks Along the Way
Ashton / Southern Boundary
The last full-service town before entering Island Park. Gas up and grab groceries here.
Mesa Falls Scenic Byway
A 28-mile loop to Upper and Lower Mesa Falls — among the last undisturbed waterfalls in the Columbia River system.
Pond's Lodge
Historic lodge and restaurant serving travelers since the early 1900s. A beloved stop for burgers and pie.
Henry's Fork / Box Canyon
World-class fly fishing access points. Box Canyon is where the Henry's Fork thunders through a narrow volcanic gorge.
Island Park Reservoir
Large reservoir popular for boating, fishing, and camping. Rainbow and brown trout abound.
Mack's Inn
The social hub of Island Park — restaurants, river access, and the famous Piano Lounge.
Big Springs
One of the largest natural springs in the world, producing 120 million gallons of crystal-clear water daily.
Johnny Sack Cabin
A hand-built log cabin at Big Springs, now on the National Register of Historic Places.
Henry's Lake / Northern Boundary
Renowned for trophy cutthroat and hybrid trout. The northern city limits end near the Montana border.
Driving the 33 Miles
Driving Island Park's main street takes about 40–50 minutes without stops. The road passes through some of the most beautiful scenery in eastern Idaho, with wildlife viewing starting the moment you enter city limits.
Moose sightings are common, especially near river crossings and willow-lined meadows. In winter, US-20 remains open and plowed, though conditions can be snowy. The corridor transforms into a winter wonderland with snowmobile trail access.
A Community Like No Other
Despite its vast geographic footprint, Island Park operates more like a tight-knit neighborhood. With ~300 year-round residents and a summer population that swells to thousands, the community has a unique rhythm.
The city sits entirely within the Island Park Caldera, one of the largest volcanic calderas on Earth (18 by 23 miles wide). It's surrounded by Caribou-Targhee National Forest, bisected by the Henry's Fork, and sits just 30 minutes from Yellowstone's West Entrance.
Visiting Island Park Today
Today, Island Park's 33-mile main street serves as the primary corridor for thousands of visitors heading to Yellowstone and Grand Teton each year. The Island Park Survival Guide covers groceries, gas, gear, and cell service along the route.
Whether you're fly fishing the Henry's Fork, riding ATVs through the caldera, or passing through on your way to Old Faithful, take a moment to appreciate the quirky history of the road beneath your wheels.
