Two agencies of the federal government publish data about the number of registered voters. The Census Bureau says there were approximately 157,596,000 registered voters as of November 2016. But the Election Assistance Commission says there were 214,109,367 registered voters at that time.
Here is a link to the EAC publication, “The Election Administration and Voting Survey”, which has that data. See page 21 (however, the page that has the page number 21 is really the 27th page in the report, when the roman numeral pages in the front are included).
Here is a link to the Census Bureau data. It is in the publication “Voting and Registration in the Election of November 2016”. See Table 4a.
Ballot Access News has determined that there were 196,167,935 registered voters in November 2016. The BAN results are from each state’s election office, and do not include inactive voters. The state-by-state breakdown will be in the July 1, 2018 print issue of BAN.
Until recently, the best data on the number of registered voters in each state was furnished by the Committee for the Study of the American Electorate, headed by Curtis Gans. But Gans died March 15, 2015, and his committee seems not to exist any longer.
Ballot Access News, starting in 1992, had published the number of registered voters in each state that has registration by party, but BAN has never had any registration data for the 19 states that don’t use registration by party.