In the fiscal year ending Sept. 30, 2017, the IRS audited roughly 1 in 160 individual tax returns. As reported in the Wall Street Journal, that represents the lowest rate--0.62 percent--since 2002, and it follows the sixth consecutive year of a decline in the percentage of individual audits.

According to the Journal, the IRS has lost nearly a third of its enforcement employees since a 2010 peak, when it audited 1 in 90 individual returns: a rate of 1.11 percent. That drop-off in staff is the result of budget cuts. Last year, funding to the IRS was at $11.2 billion, representing an 8 percent drop from its high in 2010. During the same period, the number of individual returns increased by 5 percent. In this fiscal year, the funding is increasing a bit, to $11.4 billion.

The largest decline in the audit rate was among high-income households, but they are still audited at a higher rate than households at other income levels. Last year, the IRS audited 4.37 percent of individual returns with incomes of $1 million and higher. In 2015, the agency audited more than twice as many returns reporting $1 million and higher incomes: 9.55 percent.

 
Individual income taxes represent the largest single source of federal revenue. Last year, they accounted for nearly 48 percent, an increase from 45 percent 10 years ago, according to data from the Joint Committee on Taxation, a nonpartisan committee of Congress with professional experts on staff. Corporate taxes accounted for 9 percent of federal revenue last year, down from 12 percent 10 years ago.