 California had the highest concentration with 8.64 plug-ins per 1,000 people.Hawaii ranked second (5.12) followed by Washington (4.06), Oregon (3.84) Vermont (3.73), Colorado (2.33), Arizona (2.29), and Maryland (2.03).Mississippi (0.20), Arkansas (0.28), West Virginia (0.30), Louisiana (0.31), Wyoming (0.37), and North Dakota (0.39) had the lowest concentration of plug-in cars in 2017.