The Pew Research Center recently analyzed US Census Bureau population estimates of America's population as of July 1, 2015, and they found that last year, millennials outnumbered baby boomers for the first time ever.

There is no formal definition of where the cutoffs lie for different generations, but Pew identifies five major living adult US generations:

-The Greatest Generation, born before 1928

-The Silent Generation, born between 1928 and 1945

-The Baby Boomers, born between 1946 and 1964

-Generation X, born between 1965 and 1980

-Millennials, born between 1981 and 1997

Using those definitions, Pew estimated that as of last year, there were about 75.4 million millennials, outnumbering the approximately 74.9 million baby boomers.

Pew noted that this crossover occurs as the millennial population continues to grow in size because of young immigrants moving to the US, while the boomers are aging and beginning to die off.

Here's Pew's chart showing projections for the sizes of the different generations going forward. For more, check out Pew's full report:

 Projected population by generation
Image: Pew Research Center

More from Business Insider: