It depends. In general, if you have annual online sales totaling less than $500,000 from a State, you are not considered to have "nexus" (business presence) in that State. Not all States have adopted this standard, so you may need to check at least those states where you have significant sales. Also, if you use an online sales platform (like Shopify), they may be able to help you determine if you need to claim income for any State other than where your online business in physically located.
Of course, all income is reported for Federal Tax purposes, regardless of what state generated the income.
There is not one authority for this issue, but here are two articles from reliable sources:
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