Why do Mexicans come to America when Mexico's unemployment rate is so low?

Because those statistics are very misleading: Although the official figure of unemployment in Mexico is of 3.7% (less than 2 million people), there is a considerable amount of underemployment, which is believed to be around the 26% (12 million people). This means many people work part time (instead of full-time, thus earning half the wage they need) or work for something they weren't trained or studied for, like a doctor working as a taxi driver. Also, jobs in Mexico are worse paid than most jobs in the US: for instance, a firefighter in Mexico earns a salary of some US$8,712 on average, while an American firefighter earns some US$32,748; most jobs follow the same proportion of 4 to 1 between American and Mexican wages. Thus, giving a reason for many people to try their chances entering the US illegally.