Hello @Andy-Zach and thanks for your post. Is this the number you're looking for?...
Just to disclose, i do not live in Illinois so I'm not familiar with their business tax requirements, but I did a quick search and found the following information. I hope this helps to answer your question here...
Usually each business has to register their company within the state they operate from; for example, I live and operate my business in Pennsylvania, so I had to register my business with the Pennsylvania State Revenue Dept Sales Tax. This state agency assigned me a TAX ID number to file my state sales tax I collected. I suspect the same is true for other states like Illinois. Have you registered your business with the State of Illinois to collect Sales Tax? Their website is here if it looks familiar to you. You can also file online at this site too I think.
So I think the form ST-1 tax account ID number that Illinois is requiring, isn't a number that is connected to Square; it should be YOUR company tax ID number that you would have applied for and was assigned by the State of Illinois.
The way Square handles sales tax is this; after you specify the percentage for your state collection and input into your account, when you sell a taxable item, Square POS adds the appropriate sales tax to your transaction. If your customer pays with a credit card, Square deposits that into your account: the item purchase price plus the sales tax the customer paid. So Square is just collecting and passing along that sales tax money to you...but Square does not FILE or REMIT any sales tax reports or money for you. You need to keep track through Square reports or your accounting software, and work with the State Sales Tax office to remit your business' sales tax money and report according to their schedule (monthly, quarterly, semi-annually, etc.)
