According to the Investment Company Institute, index strategies accounted for about 30% of mutual fund and ETF assets at the end of 2015. Indexing's long-term growth is especially impressive considering that index mutual funds didn't even exist until August 1976, when Vanguard launched the first one. That fund, originally named the First Index Investment Trust, sought to track the performance of the Standard & Poor's 500 Index. Today, that fund is called Vanguard 500 Index Fund, and it has assets of about $240 billion.

https://personal.vanguard.com/us/insights/article/index-rise-costs-fall-082016