Updated August 3, 2023
Las Vegas Boulevard has north and south designations.
In the north, it begins at the junction of Interstate 15 and US Highway 93. North of the interstate, it’s US93; south of it, it’s N. Las Vegas Blvd., also known as North Las Vegas Highway and NV 604. From there, it runs approximately 17 miles to downtown Las Vegas.
Just north of West Owens Avenue, it veers off to the left (N. Main Street continues straight). When it crosses the next major intersection, Washington Avenue, Las Vegas Boulevard is designated the Downtown Las Vegas Boulevard Scenic Byway by the state of Nevada.
Las Vegas Boulevard North crosses Fremont Street between Fourth and Sixth streets (which is why it used to be called Fifth Street). As soon as it crosses Fremont, it becomes Las Vegas Boulevard South.
Officially, the Las Vegas Strip starts (and the Downtown Las Vegas Boulevard Scenic Byway ends) at Sahara Avenue, though there's some disagreement about whether the Strat is one the Strip or not.
The Strip continues all the way to Russell Road, just south of Mandalay Bay.
For reporting purposes, the Nevada Gaming Commission considers "the Strip" all the hotels between the Sahara (not including Strat) and MBay, plus one mile on either side. On the west, that includes the Rio, Palms, and Gold Coast, though not the Orleans. On the east, that includes Westgate, Silver Sevens, Westin, OYO, and Virgin, plus smaller joints like Ellis Island.
The 4.2-mile-long Las Vegas Strip has been designated an All-American Road.
Beyond Mandalay Bay, the Strip turns back into Las Vegas Boulevard South, passing the Welcome to Fabulous Las Vegas sign, South Point, and M Resort.
The Boulevard continues due south till it crosses St. Rose Parkway, at which point it veers west and parallels Interstate 15 all the way to Jean. There, it skirts Jean Airport and keeps going south for another two miles, where it dead ends at the interstate.
Interestingly, NV 604 has a several-mile section west of I-15, though it’s neither connected to nor known as Las Vegas Blvd. South.
The Boulevard shows up again in Primm, running as the frontage road from Buffalo Bill’s, past Primm Valley, to the Fashion Outlets Mall, where it turns into Lotto Store Road. North of Buffalo Bill’s, the Boulevard dead-ends in the desert; it’s not connected to either NV 604 or the northern section of the road.
Altogether, Las Vegas Boulevard is approximately 40 miles long. If you include the abbreviated stretch in Primm, that adds another mile.