While there is no preexisting information to fully answer your question, I have used the available data to pull together key findings:
Shopify has provided a platform to about 600,000 businesses located is approximately 175 countries. Based on requested criteria, I have identified 17 US Shopify stores.
Below you will find a deep dive of methodology and findings.
Unfortunately, no publicly available sources revealed the total number of US Shopify stores.
Since searching direct statistics for the total number of US Shopify stores was fruitless, I tried finding the reports and articles revealing list of Shopify stores to know the rough estimate for US Shopify stores TAM. This search provided a number of articles, and blogs containing the list of Shopify stores such as — 50 Best Top Shopify Stores, Top 50 successful online Shopify stores, A — Z list of Shopify stores 2018, and Shopify Stores — Which are the Top Most Notable Stores (2017). Then, I visited each of the Shopify Store's website to know if the store meets the criteria; whether it is US based, sells things that people wear (e.g. clothing, apparel, bags, shoes), and the number of products. I easily identified the stores selling things that people wear (e.g. clothing, apparel, bags, shoes). To know if the store is US based or not, I looked at the 'Contact Us' tab or 'About Us' tab. But, no Shopify Store mentioned the total number of products they sell or their revenue. So, I tried to pick-up those Shopify stores which have many products by either looking at the product categories they have, the product types, or the number of pages they feature their products etc. I have created a final list of 17 US Shopify stores based on my research and the criteria mentioned in the request (as mentioned earlier). In addition to this, I also looked at the Shopify's corporate website to see if they have any information related to the US Shopify Stores. But, they have only provided a general information on the number of merchants they are associated with and not specifically for the US.
Below I have outlined a list of US Shopify stores, the products they offer, and their website links.
Currently, Shopify has provided a platform to about 600,000 businesses located is approximately 175 countries. It is a platform used by several trusted brands including Tesla, Nestle, GE, Red Bull, Kylie Cosmetics, and others.
TAM : US Shopify Stores
Below is a list of 17 US Shopify stores identified located in the US, selling things that people wear (e.g. clothing, apparel, bags, shoes), and have a large number products listed.
1. Taylor Stitch — This Shopify store offers products including men's shirts (casual/utility), shorts, knits, heavy bag, bottoms, denim, outwear, footwear, and accessories including cap, sunglasses, wallet etc.
2. Ugmonk — This Shopify store offers clothing including tees, crew necks & hoodies, hats, women's and kids wear. Apart from this, the store also has a collection of bags and wallet.
3. Twelve Saturdays — According to the site, they have "the most stylish gameday clothing and accessories from young and modern designers who love the game as much as they love to look unique and fabulous". This store offers products including dresses & tops, tees, and accessories such as vest, scarf, necklace and bracelet.
4. Moonbeam Baby — Since 12 years, Moonbeam Baby offers mainly kid's products including burp cloths, bibs and bib burp sets, hooded towels & wraps, blankets, tees, accessories, clothes, backpacks, lunch boxes, and bags & totes.
5. Girl Meets Dress.com — The store offers dresses of various styles for wedding, party, events, office party, and designer dresses. It also has accessories including bags, hats, and jewelry.
6. Rebel8 — The store offers products including shirts & jackets, tanks, bottoms, bags, tee, pullover, and hats. REBEL8 was started in 2003 in a small studio apartment of San Francisco.
7. Gitman Bros — The store has products like shirts of various category including classic, easy care, elite, formal, sport etc. Accessories include ties.
8. Todd Snyder — The store has a collection of clothing including dress shirts, T-shirts, tank tops, polos, sweatshirts, track suits, sweaters, coats & jackets, denim, casual pants, dress pants, sweatpants, shorts, sweatshirts, swimmers, pajamas, underwear, suits, sport coats, tuxedos, and ties. Other products include dress shoes, cuff links, and several other products.
9. Lakers Store — The store offers products for men & women clothing, and accessories. It has men's shirts, outerwear, jackets, women's shirts, outerwear, hats, bottoms, and dresses.
10. Ring to Perfection — This Shopify store has products like, rings, bracelet, necklace of various styles, and material. It also offers accessories like ties, cuff links, watches, and sunglasses etc.
11. Red Bulls — This is one of the most known brands of Shopify. The products listed on the website are men's jackets, sweatshirts, jerseys, tank tops, polos & button downs, T-shirts, and shorts. Women's wear are jerseys, sweatshirts, leggings, capri, tank tops, sports bras, and T-shirts. Other products are backpacks, beanies, scarves, eyewear, hats, watches etc.
12. Litter — It offers women accessories of different styles including bracelet, necklace, ear rings, anklets, and others.
13. Shwood — It has collection of men's and women's sunglasses.
14. Of Mercer — It offers products including dresses, blazers, jackets, tops, bottoms, knitwear, and other accessories (scarf, ear rings, necklace).
15. Gym Shark — The website has products such as bottoms & leggings, hoodies, jackets, shorts, sports bra, T-shirts, tops, underwear, and socks.
16. N2N Bodywear — They "create sexy, unique and well-fitting apparel for every kind of man, Gay, straight, big or lean". The website has a collection of clothing.
17. Packers Shoes — The store has a variety of footwear, bottoms, apparel, outwear, hats, watches, bags, and eyewear.
Based on my research, I have determined that Shopify has provided a platform to various merchants worldwide. There are many US Shopify stores which sell things that people wear including clothing for men, women, and kids wear, bags, wallets, shoes, watches, ties, and other accessories. Although, I could not find a definite number of US Shopify stores, I have provided a list of 17 US Shopify stores based on the criteria mentioned in the request.