O.C. Some cities see increases in the tens of thousands.
Immigration is only one reason for the population boom.
The video screen is flickering - flashing characters that make up lyrics as the flock joins a choir, lifting their voices in song. Services are just starting at Bethel Korean Church, and the final worshippers stream in, filling the hall by the hundreds and boosting a once-tiny congregation into one of Irvine's biggest. And Irvine is not alone. Coto de Caza experienced a jump from 103 to 693, while Tustin nearly doubled its number, from 5,260 to 10,261. One answer is immigration.