Will a state trademark protect me from someone filing a federal trademark later?

A trademark owner has common law rights in their mark as soon as they start using it. So even without a state trademark, you would have superior rights to anyone trying to use the mark after you start to use the mark. You will be protected against having to stop using your trademark if some else is granted a federal trademark registration for the same mark after you start using your mark locally. That said, it is a good idea to get a state trademark so your use of the mark shows up if anyone does a search before adopting a mark.  

The examining attorneys at the trademark office only search registered trademarks when reviewing applications for registration. If someone gets a federal trademark after you start using your mark, the owner of the federal mark would not be able to stop you from continuing to use your mark. However, you would not be able to expand your operation into new states or expand what you do into different areas outside what you are already doing. This is especially true if the new area comes close to the good/services of the owner of the federal trademark.  

The keyword about your common-law rights is your use must be before someone else files or uses the same mark for the same or similar goods/services. You can check the trademark office database to see if there is a federal trademark registration for your mark.

We offer trademark screening searches that check state and federal trademark databases as well as the internet.  A trademark screening search is helpful to search for marks that are similar but not identical to your mark. A trademark-screening search will also search beyond your particular goods and services.