Boston, Detroit, New York, Miami, Washington DC, Philadelphia, Minneapolis, Denver, Dallas, Chicago, Los Angeles.
If you use MSA population, Denver would have the smallest population at about 3.0M, followed by Minneapolis (3.7M), Detroit(4.3M) and Boston (4.9M).
Austin is back at 2.5M and Salt Lake is way down the list at 1.3M
In the United States, a metropolitan statistical area (MSA) is a geographical region with a relatively high population density at its core and close economic ties throughout the region. Such regions are not legally incorporated as a city or town would be and are not legal administrative divisions...
https://en.m.wikipedia.org/wiki/Metropolitan_statistical_area