We see a flashback to when Kagami lived in the US in episode 1 of season 2 (26Q).
Judging from all the palm trees, I'd hazard a guess that he'she was probably in California. OnCalifornia also seems like the most likely option on a demographic basis (i.e. where are Japanese temporary immigrants most likely to end up?), California seems like the most likely option.
Is it ever explicitly stated where he liveslived? And if it is California, is it ever stated whether he's in SoCal or NorCal (or somewhere else)?