Where do I find a list of all the tags and categories I've used to date?

Hi @Mountainmint, 

While there isn't a centralized place where you can find all the categories and tags that are used throughout your site, the Advanced tab of each page's settings show all the categories/tags in use on that page. Have a look into this Squarespace help article for more details:

Categories and tags - Bulk-edit categories or tags

Fell free to reach out to Squarespace Customer Support for any further questions you might have about managing categories and/or tags on your site.