Creeping phox is blooming for me and I've seen butterflies nectaring on that in the past - none this year so far though. Verbena Homestead Purple has a couple flowers but normally doesn't bloom this early. It has a very long bloom time and sometimes attracts butterflies. I wish both were taller. I have a few other things blooming but none that I've ever seen butterflies on.
I think my woodland phlox will be blooming pretty soon and the butterflies like that. The weather is so unusual this year. I have quite a few plants still sleeping.

I posted a reply on an old thread so it will come back to the first page. You might find some helpful info in that one too. It's titled "Best spring blooming perennials & best zinnias for butterflies"

I've seen butterflies on my phlox, Osmanthus fragrans, and viburnum...so far.

It's a bit aggravating, but they always seem to find some dandelion flowers.

Try Phlox divaricata-Wild Sweet William, Bluebells and Senecio obovatus (invasive)They are all blooming in St. Louis.

Lots of good suggestions here. Here's another suggestion for your consideration. The Siberian Wallflowers - Cheiranthus allionii I began last season from seed (a new plant to me) are blooming their little heads off right now so I think I can safely say they are an early spring bloomer. The fragrance is WONDERFUL, too.

They overwintered on the deck in a big pot, never dying back and as soon as it warmed a bit, they began putting up their little flower buds. Easy to start from seed and a nice size to tuck in among other late emerging plants to provide nectar for the early winged travelers. I learned about them from the director of the Dallas Arboretum & Botanical Society. Plants that do well in that area tend to do well in my area. It is a biennial.

Happy spring to all...

Mary

Here is a link that might be useful: Thomas Jefferson - Monticello gardens

Today I was at Lowe's, and a yellow female tiger swallowtail was nectaring feverishly on their purple lantana. This reminded me that I usually buy some nectar plants, usually pentas, at this time of year, because they've all been in green houses and are set out to sell because they're blooming.
But the butterflies will usually find nectar on their own. My big locust tree is in beautiful full bloom now, and butterflies are nectaring on it, as well as the red pentas already planted in my garden. They also nectar on weeds, like KC said, such as flea bane, which is everywhere. And with all this rain we've had - I've had 6.4" in the past two days - they can probably get minerals and other nutrients just from "nectaring" in the wet ground.
Sherry