Who Must File
Colorado requires all businesses in the state to register their trade names if they operate under a different name from the legal name. For example, if your name is John Doe, but you operate Corner Shop Cookies as a sole proprietor, you must register the name "Corner Shop Cookies" as your trade name with the secretary of state. The only exception is for nonprofit entities, which are not required to register trade names as long as they have filed articles of incorporation or some other formative document with the secretary of state.
Trade names must be filed online through the secretary of state's website. From the "File a Business Document" page, select "File a form to create a NEW record" and click "Trade Name" under the "LLCs, Corporations & Trade Names" heading. Select the correct business entity to get the appropriate trade name registration form for your business. When filling out the form, include your name, contact information, trade name and brief business description. You can also specify whether you want the trade name to take effect immediately or on a date up to 90 days in the future.
The length of time your trade name is valid depends on the type of your business. General partnerships and sole proprietorships must renew their trade name every year -- and they can renew during the last three months before the expiration date. For corporations and LLCs, the trade name remains in effect as long as the business is in good standing. If the business becomes delinquent, such as if it doesn't satisfy the annual reporting requirements, or if it dissolves, the name is only protected for one year after the delinquency or dissolution.
In Colorado, registering your trade name merely offers notice that you're using the trade name -- it does not provide name protection. When registering your name, there's no requirement that it be distinguishable from any other previously registered trade names, so it's possible that your desired trade name is already in use by another business or that another business will register the exact same trade name in the future. Other laws offer name protection, however, such as the Colorado Consumer Protection Act, prohibitions on unfair competition and federal trademark registration.