Quite a few books have been published on this subject, books that illustrate what plants are safe to eat, along with where they grow in the country. You can also get region specific books and Lee Allen Peterson has a book titled "A Field Guide to Edible Wild Plants: Eastern and Central North America." This book is available here (via Amazon) and would cover most of the edible plants in Kentucky. You can also view all the books on wild edible plants here (via Amazon), and there are free ebooks that I have posted on this very subject you can download from here and here.
Trails.com has a guide posted that lists a few common wild edible plants in Kentucky that must of us could probably already identify. Here is their findings:
Tubers and Bulbs
The best of the wild tubers is the wood sorrel, or oxalis. The plant has a root tuber similar to a small potato. However, the stems, leaves and flowers are mildly toxic and should not be consumed. Ordinary onion grass, which grows virtually everywhere in Kentucky, is also edible. This includes both the grassy stem and the bulbs. Spring onions, or "ramps," are also easy to find and can be eaten.
Fruits and Berries
The most common wild berry in Kentucky is the blackberry, the briars of which can be found fringing numerous farms and vacant suburban lots. The American elderberry is also found in the state, but it should be carefully studied before consumption since it superficially resembles several varieties of poisonous berries. The ill-informed can easily make a mistake and quickly come to regret it. Ground cherries are also present in Kentucky, but since these plants thrive on bad, well-watered soil, it would be best to look for them in the sandy and/or rocky areas around the state's creeks and rivers.
Vegetables
The ponds and lakes of Kentucky are home to wild watercress, which can be harvested and eaten. Often mistaken for thistles, wild prickly lettuce is just as edible as its domesticated counterpart and arguably tastier to boot.
Nuts
Walnuts in Kentucky can be had from the American black walnut tree, which needs plenty of water and good soil. It, therefore, grows best close to rivers and streams. The state also has a good climate for hickory trees, which produce edible (and often ignored) nuts. The Kentucky coffee tree produces a semi-edible product, meaning that the seeds can be used as a substitute for coffee if they are roasted for three or four hours. However, even after being roasted, the seed remains marginally toxic and should never be consumed in large quantities.
Other Plants
Chickweed is a wild herb that can provide some nutrition if consumed, and the entire plant is edible. The ordinary, humble dandelion has long seen its flower petals used for making tea and recently has become popular for use in salads. It is easy to find and can be eaten straight from the field.