It peaked in 1999.
That actually depends on the sector of the border you're talking about.
Right now, the Tucson sector is the busiest along the southern border. In the first 5 months of FY '06 (Oct-Feb) we've seen 42,000 apprehensions per month.
Last year saw the highest number of apprehensions in this sector, ever, and this year is on track to outpace '04.