Please read Vanguard's How America Saves 2017: Vanguard 2016 defined contribution plan data published June 1, 2017. Here are a few quotes from the report:
"Defined contribution (DC) retirement plans are the centerpiece of the private-sector retirement system in the United States. More than 94 million Americans are covered by DC plan accounts, with assets now in excess of $7 trillion. Vanguard is among the leaders in the DC marketplace with more than $1 trillion in DC assets under management as of March 31, 2017."
"Participant contributions to equities were unchanged in 2016 at 74%. In 2016, nearly half (49%) of all new contributions to these plans were directed to target-date funds."
"Use of target-date strategies in DC plans continues to grow. Nine in 10 plan sponsors offered target-date funds at year-end 2016, up over 50% compared with year-end 2007. Nearly all Vanguard participants (97%) are in plans offering target-date funds. Seventy-two percent of all participants use target-date funds. Two-thirds of participants owning target-date funds have their entire account invested in a single target- date fund. Forty-six percent of all Vanguard participants are wholly invested in a single target-date fund, either by voluntary choice or by default."
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Source: Vanguard's How America Saves 2017: Vanguard 2016 defined contribution plan data