Trump claims media 'dishonest' over crowd photos
Trump was speaking after photographs were published appearing to show more people attended the inauguration of his predecessor Barack Obama in 2009.
Mr Trump's press secretary said it had been "the largest audience to ever see an inauguration" even though figures he cited add up to under 750,000 people.
He said the new US administration would hold the media accountable.
On Jan. 21, millions in the US and around the world took part in protests to highlight women's rights, which activists believe to be under threat from the new administration.
In response, President Trump tweeted on Sunday: "Watched protests yesterday but was under the impression that we just had an election!
"Why didn't these people vote? Celebs hurt cause badly."
The largest US rally was in the capital, Washington DC, which city officials estimated to be more than 500,000-strong, followed by New York with some 400,000 and hundreds of thousands elsewhere, including Chicago and Los Angeles.