WASHINGTON — Americans last year reaped the largest economic gains in nearly a generation as poverty fell, health insurance coverage spread and incomes rose sharply for households on every rung of the economic ladder, ending years of stagnation.

The median household’s income in 2015 was $56,500, up 5.2 percent from the previous year — the largest single-year increase since record-keeping began in 1967, the Census Bureau said on Tuesday. The share of Americans living in poverty also posted the sharpest decline in decades.

The gains were an important milestone for the economic expansion that began in 2009. For the first time in recent years, the benefits of renewed prosperity are spreading broadly.

The data was released into a heated presidential race, where Democrats seized on the statistics to promote Hillary Clinton’s candidacy and undercut Donald J. Trump’s dark assessment of the nation’s well-being.