State officials are still trying to figure out how to regulate the new industry, and shops are not expected to open until at least January 2014. But Douglas County's ban takes effect Thursday.
The ban would impact only pot stores and commercial growing operations, not personal use of the drug.
The Denver Post reports that the county is the first in the state to approve a complete ban on pot operations.
The Colorado Department of Revenue is expected to have rules for the industry after July 1. The Colorado Municipal League says many other cities and counties are likely to wait until then to decide on bans.