If you live in the United States, you should know about the USDA Plants Database!

Identifying what plants are actually native to your area can be surprisingly tricky. A lot of info out there is state- (or even less helpfully, region-) specific, but if you live in a large and/or geographically diverse state what's native in one corner may be completely foreign in another. There's also a lot of information out there that's too vague or straight-up incorrect, especially for any plant with numerous common names or multiple sub-species.

Enter the USDA Plants Database! While far from perfect, it is hands-down the best tool I have encountered for verifying what plants are native to an area of the US down to the county level.

I often use the database to cross-reference plant guides and recommendations, such as relating to pollinator-friendly gardening. For instance, you would be really surprised how often plants that are not actually native to your area will slip into "native" seed mixes! On the flip side there are also lots of plants that are native to large regions that are often overlooked because they're not a regional specialty, such as selfheal (Prunella vulgaris), which is native to much of the northern hemisphere.

Many of the more common plants, such as selfheal, have two-page writeups in the Plants Database that have an admittedly agricultural bent to them, but can still be quite helpful for home gardeners too (continuing with the previous example, here's selfheal's). I highly recommend giving them a read, especially if you want to grow your plants from seed or propagate them.

Unfortunately the database is not fully populated (some entries are more info-rich than others), and things can get a little confusing when all you have is the common or even scientific name for a plant that has many subspecies (or even worse, if the scientific name has changed at some point), but that's more an issue with taxonomy than the database. If in doubt, checking the images tab can be quite helpful in verifying you have the correct plant entry. Still, I have yet to find any source as comprehensive and accurate as this one.