That's for overstaying a visa. A large number of illegal immigrants simply arrive illegally. Page 5 in this document shows numbers, with Mexico at the top. [1]

That's for overstaying a visa. A large number of illegal immigrants simply arrive illegally. Page 5 in this document shows numbers, with Mexico at the top. [1] And here is another source showing almost the same numbers (i.e, Canada nowhere in site). [2] [1] https://www.dhs.gov/sites/default/files/publications/18_1214_PLCY_pops-est-report.pdf https://www.dhs.gov/sites/default/files/publications/18_1214... [2] https://www.migrationpolicy.org/data/unauthorized-immigrant-population/state/US https://www.migrationpolicy.org/data/unauthorized-immigrant-...