See this interesting article from a Colorado newspaper on dispute between Boulder, Colorado and a company that helps facilitate gameday housing rentals between property owners and third party guests.
The City of Boulder has taken a pretty firm stance that any non-hotel entity that seeks to rent properties to tenants for less than 30 days is violating city zoning ordinances which prohibit short term rental properties in residential areas.
However, I spoke with someone at GamedayHousing.com over the phone and they claim that while some cities have called the practice illegal, no locality (including Boulder), has ever sent sent them a notice of violation or proceeded beyond threats. The claim the practice is entirely legal and that they continue to operate in Boulder to this day.
It is very much worth your time to study your own city or town code as they all vary individually. It's also worth your time to contact City of Boulder officials to follow up on these findings, as the article was written 5 months ago and is heavily disputed by the company involved.
City of Boulder
Boulder, Colorado 80302
Hope this helps you get started,