The largest Auto Parts store in the US is AutoZone which is a retailer of aftermarket automotive parts and accessories.
AutoZone was founded in 1979 and has 7,140 AutoZone stores across the United States, Mexico, Puerto Rico, Brazil and teh US Virgin Islands.
AutoZone is based in Memphis Tennessee.
The best place to buy auto parts online is RockAuto, eBay, Partsgeek.com and Amazon.com
These are the places where I buy my auto parts from.
Most auto parts I buy from eBay although sometimes I can only find the auto parts I need at RockAuto, Amazon or Partsgeek.
You can get most auto parts online cheaper than you can in an auto parts store.