1) "Idaho The longest main street in America, 33 miles, in Island Park" Source and further information: http://www.infoplease.com/ipa/A0770175.html 2) "For years, it has been said the longest continuous Main Street in the United States is located right here in the Metro East area. The city of Belleville, Illinois has been recognized as having the longest continuous Main Street, being 13 miles long, one way. If you’re an avid runner, run Belleville’s Main Street both ways and you have just run a marathon! Of course varying opinions begin to surface during research of the longest roads in the United States and world. Another site named Boise, Idaho as having the longest Main Street in the United States, being 33 miles long. Maybe the key difference between Belleville’s longest Main Street and Boise’s longest Main Street is Belleville’s Main Street is continuous. According to www.history.com, O Street in Lincoln, Nebraska ranks as the longest Main Street in the nation at 59 miles. Can you imagine traveling 59 miles on a Main Street? Hopefully there aren’t too many stoplights! Traveling from the longest Main Streets to the longest streets, there are even more varying opinions. Broad Street in Philadelphia has been said to have the longest street in the United States, measuring 12.5 miles. Some reject this idea because the town’s city hall interrupts Broad Street somewhere in the middle. Another website said some sources claim Western Avenue (23.5 miles) in Chicago as being the longest street in the world. Other opinions reflect Colfax Avenue in Denver, CO, Figueroa, in LA, or even Broadway in New York as having the longest Main Streets. One website identified Colfax Avenue as the longest commercial street in the United States. According to www.wikipedia.org, West Colfax Avenue began as a trail during the Colorado Gold Rush, being a well-traveled route to the mountains’ gold fields. The existence of West Colfax Avenue has been confirmed as far back as the spring of 1859 when it became a major thoroughfare for goods, people and transportation service to and from the Colorado Mountains. Speaking of the longest commercial street, for those of you who really enjoy shopping, the longest outdoor sale is claimed to be along the 127 corridor from Defiance, Ohio through Kentucky, Tennessee and ending at Gadsen, Alabama. Yes, 630 miles of pure hard core sales and shopping. The world’s longest outdoor sale includes commercial sales and yard sales and will occur this year August 7 – 10." Source and further information: http://www.haengr.com/Newsletters/newsletterApril2008_02.htm Further information: http://en.wikipedia.org/wiki/Colfax_Avenue

Depends upon how you define it, but I'm going with Broad Street in Philly

Colfax Ave is the longest continuous street in the in the world, but it is longer than the Denver Metro 26 Mile Marathon. Colfax starts in Golden, CO at Mt Vernon Canyon Rd & W Colfax Ave and ends in Strasburg, CO at E Colfax Ave & Headlight Rd. Google Map the start and end points, move the route to stay on Colfax and you get 50.7 miles. Playboy Magazine once called it the longest and wickedest street in America because it was once a haven for prostitution. Since cleaned up by Denver metro Police Departments.