Election Day registration is currently available in eight states—Idaho, Iowa, Maine, Minnesota, Montana, New Hampshire, Wisconsin, and Wyoming—and the District of Columbia. North Carolina allows same-day registration during its early voting period, but a new law, to take effect in 2014, will repeal that provision. California, Colorado, and Connecticut have passed laws instituting Election Day registration in the coming years.
Recent data from the Election Assistance Commission and its biannual survey of voter registration, however, show 10 additional states recorded same-day registrations in 2012.
There are clear explanations for some states:
In other states it is less clear what occurred: