Retirement assets held by Americans continued to grow in the first quarter of the year to a total of $24.9 trillion, up 1.3 percent from $24.6 trillion at the end of last year, according to the Investment Company Institute, a nonprofit organization representing funds and their investors based in Washington, D.C.

Retirement assets accounted for 36 percent of all household financial assets in the United States as of March 31, ICI says. Assets held in retirement accounts have continued to grow each year since hitting a low of $14.2 trillion in 2008.

Most asset categories and fund types increased with the exception of government-sponsored defined benefit (DB) plans, which declined 0.5 percent to $5.1 trillion.

Assets in individual retirement accounts (IRAs) increased 2.1 percent to a total of $7.6 trillion at the end of the first quarter. Most retirement assets are held in IRAs, with defined contribution (DC) plans coming in second.

Americans held $6.8 trillion in all employer-based DC retirement plans at the end of the quarter, of which $4.7 trillion was held in 401(k) plans, ICI says. Both represent slight increases over the end of 2014.