Start by going to The US Trademark website search portal
here. Click on “Search Marks”, #2 in the middle blue box.
Now click on “New User Form Search (Basic)”
Enter your Company Name idea in the “search term” box and, using the drop-downs, make sure you choose “ALL” and “All search terms (AND)”. Then Click “Submit Query”.
If your company name shows up, just click on it in the word mark column to see the results.
You also want to check with your local county clerk’s office to make sure no one in your area is using the name. You can look up the number to call on your county website.
~C
PS-
I learned how to do all this when my Company name was challenged by someone in Germany who had "Vital Office" trademarked here in the US.
After much searching & researching he had no basis to request I change my name. Long story short- I was lucky.
If I had done all this in the beginning I would've went for another name altogether.