The easier way to create isometric grid:
1. Add a Line with the Line tool;
2. Select Line created > Effects > Distort and Transform > Transform;
3. Use “Move” – 30px for the artboard ~1500x1500px, Copies: 130;
4. Object > Expand appearance;
5. With selected group, double-click on the Rotate tool > Angle: -60% > Copy;
6. Select first group, double-click on the Rotate tool > Angle: 60% > Copy;
7. Select 3 groups, Ctrl (Cmd) G to group them;
8. Change border color;
9. Create Rectangle with the width/height of artboard, e.g. 1500x1500px, align to artboard;
10. Select group with the new rectangle > Right click > Make clipping mask;
11. Lock the layer and create your perfect isometric illustration!