Ethnic Tatars comprise the majority of the IDPs, but Ukrainians, Russians and mixed families are included in the total, the U.N. High Commissioner for Refugees spokesman Adrian Edwards said.
"Among the affected population are people who have been displaced twice, first from Crimea, and then again from the eastern part of the country," Edwards explained.
He added about a third of the total IDPs are children.
Most of the refugees went to western and central Ukraine, fearing persecution, and many received direct threats. Few have sought asylum in other countries.
Edwards noted most of the displaced are in shelters or in privately owned facilities, including sanatoriums and hotels, but "the capacity of host communities to support people is fast becoming exhausted."
The U.N.'s estimate comes on the heels of a U.N.-backed report, which estimated that violent conflicts led to 33.3 million IDPs worldwide in 2013.