What in the world does "majority-minority" mean? This is a term used by the Census Bureau to designate a county as having 50% or more of its residents falling in a minority group. Denver, CO is the largest county to join the 303 other counties where the majority of the population is a minority (from this press release).
Where are they getting these numbers? From the Population estimates that are put out by the Census bureau every year. (They also inform the ever-changing population clock.)
Still want more demographic data? Check out the library's guide.