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US Mint Philadelphia, PA US Mint West Point, NY US Mint Denver, CO US Mint San Francisco, CA
You can buy directly from the US Mint, not the indivdual mint locations.
The US Mint was created by Congress and makes circulating coins. To apply for a job with the US Mint a person can apply at the USAjobs.gov website.
US Coins with no mint mark were minted at the US Mint's main facility in Philadelphia, Pennsylvania.
The closest US mint would be the San Fransisco mint.