Image of 7 For All Mankind’s factory via GoRuck.com.
Jeans are made in many parts of the world, the top places being the United States, mainly Los Angeles, Italy, China, Turkey and Japan. Los Angeles is famous for its premium denim factories as is Italy. China and Turkey are famous for the everyday brands and Japan is known for its raw and selvedge denim, however different jeans can essentially be produced in many places. Some are even made in England, Portugal, France and all over the world.
Jeans are made in factories of various specialties. Premium denim, from the likes of brands such as Diesel, 7 For All Mankind, J Brand and Paige etc, are made in specific jeans factories which have workers trained in premium denim making and use a lot of special equipment to get the cuts, finishes, chain stitching and normal stitching perfect. Cheaper jeans can be made in the normal garment factories alongside other clothes as they don’t require a specific amount of detail. Premium jeans also go through their washing process in specific wash houses where they are hand sanded and creased, stone washed, coated in resin or wax and hand distressed etc. You can see a couple of videos of how jeans are made in the links below.