  Understanding disorder in graphene is essential for electronic applications;
in contrast to conventional materials, the extraordinarily low electron-phonon
scattering1, 2 in graphene implies that disorder3-7 dominates its resistivity
even at room temperature. Charged impurities5, 8-10 have been identified as an
important disorder type in graphene on SiO2 substrates11, 12, giving a nearly
linear carrier-density-dependent conductivity {\sigma}(n), and producing
electron and hole puddles13-15 which determine the magnitude of graphene's
minimum conductivity {\sigma}min10. Correlations of charged impurities are
known to be essential in achieving the highest mobilities in remotely-doped
semiconductor heterostructures16-18, and are present to some degree in any
impurity system at finite temperature. Here we show that even modest
correlations in the position of charged impurities, realized by annealing
potassium on graphene, can increase the mobility by more than a factor of four.
The results are well understood theoretically19 considering an impurity
correlation length which is temperature dependent but independent of impurity
density. Impurity correlations also naturally explain the sub-linear
{\sigma}(n) commonly observed in substrate-bound graphene devices2, 11, 12, 20.
