The only US city with only vowels in its name is Aiea, Hawaii. Another city with only vowels in the name is Eiao in Marquesas Islands.
There is only one city in the US called Newport News and that is Newport News, Virginia.
There are 2: Oklahoma City, Oklahoma. Indianapolis, Indiana
Olympia is the capital city of the U.S. state of Washington.
Miami is not a city name special to only the US. There is a Miami in Australia, Canada, and even Iran (also spelt Meyami).
Circleville, Ohio is one
Salt Lake City, Utah.
Salem In Tamilanadu
Vancouver is a city in Washington State. It is the only city in the United States with the name Vancouver.
Washington, D.C. is the only city not a part of a state. However, it is still in the US.
the only one I can think of is Memphis
A US city starting with I is Indianapolis, IN.