This is an excellent graphic giving a visual representation of where the cartels are, and a general idea of their activity. If you click on the image, you should be able to get a bigger picture of it and really dig into the data. All of this data was extracted from reports issued by the Justice Department’s National Drug Intelligence Center. The 1,286 number is startling.  No telling how many more cities have reported since 2010? Here is a quote:

The numbers could rise in coming years. The Justice Department’s National Drug Intelligence Center estimates Mexican cartels control distribution of most of the methamphetamine, heroin and marijuana coming into the country, and they’re increasingly producing the drugs themselves.
In 2009 and 2010, the center reported, cartels operated in 1,286 U.S. cities, more than five times the number reported in 2008. The center named only 50 cities in 2006.
Target communities often have an existing Hispanic population and a nearby interstate for ferrying drugs and money to and fro, said author Charles Bowden, whose books on the Mexican drug war include “Murder City: Ciudad Juarez and the Global Economy’s New Killing Fields.”
“I’m not saying Mexicans come here to do crime, but Mexicans who move drugs choose to do it through areas where there are already Mexicans,” he said.

Also, if you are wondering what happened to the DoJ’s National Drug Intelligence Center, it was closed and folded into the DEA recently. But you can still read through their archives here. –Matt