DO NOT eat a berry if you cannot identify it. I decided not to include the obvious blueberries, blackberries and raspberries, but this guide will assist you in identifying which wild berries are, in fact, poisonous.
The best way to stay safe when looking for berries is keeping a berry guide, like this one, with you while you gather them.
red or blue berries on evergreen shrub with soft bright green needles; if you must eat for survival just the fruit of the yew but never the seeds; soft red capsules with a hard green stone in the center; eating more than three yew berries can cause vomiting, abdominal pain, dizziness, difficulty in breathing, and changes in heart rate
HOLLY berries - poisonous
Hard, red berries that grow on deciduous or evergreen shrubs (these shrubs can grow to be a tree); leaves are stiff with sharp points and may be edged with white; eating more than 3 holly berries can cause severe and prolonged nausea, vomiting and diarrhea, as well as drowsiness
(European Holly ) A different plant from holly, European holly berries are slightly poisonous to people. They have white flowers and red berries.
DAPHNE berries - poisonous
sweet smelling green or pink flowers
PRIVET berries - poisonous
berries of this shrub are only mildly poisonous to humans (but eating them is still not recommended), has purple to black fruit
POKEWEED berries - poisonous
A.k.a. Ink berries, poke, poke berry and pokebush; birds can digest pokeweed but the berries are poisonous to humans; berries are dark purple, while the flowers of are greenish-white; grow up to five feet tall and has thick green-purple stems similar to rhubarb; grow in clusters, like grapes, and ripen from white to green to rose and finally purple; Ripe berries stain the hands purple when crushed; eating over 10 berries may cause headache, abdominal pain, and severe diarrhea
JERUSALEM CHERRY - Poisonous
resembles a cherry tomato, making it easily confused for a non-poisonous fruit
ELDERBERRY - Poisonous
produces white or cream colored flowers and black, blue-black or red berries; contains cyanide; Instances of cyanide poisoning include symptoms ranging from gastrointestinal distress and diarrhea to a general feeling of debility; Cooking the berries dispels the cyanide toxicity
DOLL'S EYES - poisonous
highly poisonous berry which grows on a plant with white flowers. The berry itself is large and white with a black mark, giving it the appearance of eyes.
AMERICAN BITTERSWEET berries - poisonous
woody vine often used in fall wreaths and dried flower arrangements; orange-yellow berries are three-part capsules with a seed in each part; they grow at the point where the leaves join the stems; eating American Bittersweet berries can cause stomach upset and diarrhea
JUNIPER berries - poisonous
evergreen tree often used in holiday decorations; blue-purple berries have been used in recipes for flavoring; safety of juniper berries as a food item is questionable since abdominal cramps and diarrhea have been reported when large amounts were eaten
DOGWOOD TREE berries - Not Poisonous but watch out
spring flowering tree which bears pink or white flowers; in fall there are bright red berries; Dogwood berries are not toxic when eaten, but there have been reports of rashes after skin contact with the tree
HONEYSUCKKLE berries - Not poisonous
woody climbing vine that produces sweetly fragrant white or yellow flowers; suck the honey from the flowers in the spring; in fall there are red or orange berries; Neither the flowers nor the berries are reported to be poisonous
PYRACANTHA berries - not poisonous but watch out
A.k.a. "Fire Thorn" because the thorns can cause an irritating rash; evergreen shrub with orange-red and yellow berries which grow in clusters; Pyracantha berries are not considered poisonous unless large amounts are eaten; some sources even report them to be edible
WILD STRAWBERRIES - not poisonous
wild version of the edible strawberry; looks exactly like the strawberry you may find in a grocery store, but the taste is not as sweet; wild strawberries are not poisonous and they can be found in the spring, summer and fall