What promises to be a mundane mortgage fraud trial filled with dry testimony from bankers about decade-old financial documents drew a standing room-only crowd to a federal courtroom in Chicago on Tuesday morning.

The reason? The defendant is a judge herself.

Cook County Associate Judge Jessica Arong O’Brien is the first sitting judge in years to face a jury on criminal charges at the Dirksen U.S. Courthouse.

O’Brien, 50, was accused of orchestrating a $1.4 million mortgage fraud scheme stemming from the purchase of two South Side properties when she was a lawyer and real estate agent a decade ago — long before she became the first Filipina elected to the county bench.

If convicted, O’Brien, who was reassigned to administrative duties following her indictment last year, would by law be forced to step down from her judgeship.

In opening statements Tuesday before…