Google auto detects your location to display local search results. If you are in US you will get results according to your locality i.e(results from United States).
you will see google domain with country code (google.com.us) but if you have travelled to any other location like Australia, you will automatically see (google.com.au) and start getting local search results from Australia.
Now these local search are irrelevant to you, as you belong to US and interested to see result from US. To achieve this you need make some changes in setting then look for “Regions for Search Results” and set you location you want results from.