Starting the day in the War Room full of concept art for the film, executive producer Deborah Snyder confirmed that the creatures seen in Dawn of Justice were Parademons, and they'll be back with different looks in Justice League. Concept art showed two versions of the creatures - one was mostly green and, the other, mostly brown.
The Parademons nest up in a ventilation tower on Stryker's Island which becomes a major action sequence involving Batman, The Flash, Wonder Woman, and Cyborg as they hunt for missing scientists (including the head of S.T.A.R. Labs, Silas Stone). To start the scene, the creatures appear to be hanging like bats in the underground hideout. Counting them would have taken too long, so we'll just have to say there will be "a lot" of Parademons in the film. Luckily for Batman and company, they don't look to stand all that much of a chance against his new tech, like the Crawler which will be spewing flames and bullets at them.
The Parademons involvement in Justice League is only a further hint towards Darkseid's eventual appearance. We've suspected the big bad would show up eventually, especially after the Omega symbol was laid out in front of Batman during his dream sequence in Dawn of Justice, but with Steppenwolf confirmed to be the villain in Justice League, his nephew can't be too far off.
Justice League is set for release November 17, 2017.