Goldwater did very well in the Chicago suburbs, which were very much a Republican bastion at the time. This is what kept Johnson under 60%. Moreover, Cook County was not as heavily Democratic then as it is now-Johnson got in the sixties there, whereas Hillary Clinton, for example, broke 70% in 2016.Pretty much this, plus 1) Cook County wasn't quite as urban then (the Cook suburbs seemed to have voted a lot more like the Collar Counties do now, and the Collar Counties voted a lot more like McHenry County now) and therefore less Democratic, and 2) Southern Illinois' ancestrally Democratic lean was more akin to that of Kentucky than that of Mississippi and therefore much, much more likely to stick with LBJ.