SPRINGFIELD — State income tax revenue growth in September continued to exceed the rate of the income tax increase approved earlier this year, according to figures from the Legislature's Commission on Government Forecasting and Accountability.

Last month the income tax brought in $1.4 billion, or 77.4 percent more than it did last September, according to COGFA. State legislators approved a 67 percent increase in the income tax in January.

And the trend is improving, based on a review of past COGFA monthly reports. Comparative income tax growth was 67.9 percent in June, 67.7 percent in July and 68.2 percent in August.

Further, the state sales tax — which was not increased by the Legislature this year — also is displaying robust growth. It was up 16.3 percent in September, after growth rates of 8.2 percent in June, 11.8 percent in July and 11.7 percent in August.

But the monthly report accompanying the revenue numbers urged caution and suggested that the revenue growth may not continue.

"While the economic sources have met the (COGFA) expectations to date, the forward view of revenues should be tempered with the realization that some clouds on the horizon will serve to stymie a repeat of similar growth," wrote COGFA revenue manager Jim Muschinske.

No longer will revenue get a boost from last year's tax amnesty program, Muschinske said. Further, the Illinois economy will be affected "if the current economic soft patch continues to be accompanied by stubbornly high unemployment. Looking ahead, continued economic malaise would jeopardize even modest revenue expectations well into (fiscal year) 2013," which begins next July.

Although all state-source revenue was up more than 30 percent last month, federal funding was down more than 46 percent. Overall state and federal general funding was up 13.3 percent from a year earlier.

Both lottery (up 11.3 percent) and riverboat casino transfers (up 105 percent, likely the result of the recent opening of a 10th casino, in Des Plaines) reported healthy gains.