In the Philadelphia region, Chester County is where the money is.

Chester County ranked 21st among the more than 3,100 counties in the United States by adjusted gross income for 2007, according to a new analysis of IRS data by the Transactional Records Access Clearinghouse at Syracuse University.

(I hope everyone's comfortable reading about adjusted gross income — you know, line 37 on Form 1040. It is the height of tax season, after all.)

Chester County, with average adjusted gross income of $96,578, was wedged between No. 20 San Mateo County in California ($96,775) and No. 22 Howard County in Maryland ($95,670). What's remarkable is that Chester County's AGI is nearly $16,000 higher than it was in 2003.

In that same span of time, the City of Philadelphia's average AGI went from $34,886 to $39,660. It's much harder to move that average given that Philadelphians filed 572,498 federal income tax returns in 2007, compared with 196,256 for Chester County residents.

Also among the 50 wealthiest U.S. counties is Montgomery County (No. 41) at $86,685. Five New Jersey counties were in the Top 50; all are north of Burlington County, which had a 2007 average AGI of $71,763.

Here are the stats for the other three South Jersey counties in our region: Gloucester ($63,807), Camden ($58,857) and Salem ($56,273).

Bucks County's average AGI hit $77,180 in 2007, while Delaware County's weighed in at $69,181.

What was the top county in terms of adjusted gross income? Goochland County, an exurb of the Richmond area of Virginia. Its average AGI was $137,045, far surpassing the $126,998 of Teton County, Wyoming, (think: Jackson Hole, ranchland for the wealthy, and Yellowstone National Park) and Fairfield County, Connecticut (likely turbocharged by the presence of so many hedge fund managers), at $117,425.

At the other end of the income spectrum is St. Bernard Parish in Louisiana at $9,959. The researchers called it a statistical outlier, because the area is still recovering from Hurricane Katrina in 2005. Second from the bottom was Jackson County, South Dakota, at $17,655.