I agree. Blackberry or dewberry of some type.

Characteristic unripe fruits are actually present and visible in the photo. Poison ivy does not make blackberries

Thank you!

Thanks! I don't see any unripe fruit, but maybe I don't know what to look for.

In the last photo, at approximately one o'clock (if your photo was a clockface), there is a cluster of immature berries and a larger but still unripe one at about 4 o'clock.

When you first posted this in July a few years ago, berries in some stage of development would be expected. Don't expect to find any in April :-)

First there will be flowers, then berries.

Here’s poison ivy intermingled with English ivy and Virginia Creeper (not shown, but it was all over) on the ground