Immigration on re-entering US from Mexico?

[subbu42]

Hi

My wife (who is on an H1B visa) is flying to Mexico from Detroit on work. On her return flight to DTW, will she need to pass through immigration at DTW airport, or will she need to go through that in Mexico?

Thanks.

[txh1b]

Only Canada has pre-boarding Immigration. It will be in DTW upon return from Mexico.

[subbu42]

thank you for your help