It will also close two compounds used for Russian intelligence-gathering.
President Barack Obama had vowed action against Russia amid US accusations it directed hacks against the Democratic Party and Hillary Clinton's campaign.
Russia has denied any involvement and called the decision "ungrounded".
The US state department declared the 35 Russian diplomats from the Washington DC embassy and the consulate in San Francisco "persona non grata", and gave them and their families 72 hours to leave the US.
