How many Pentecostals and Charismatics are there in the U.S. today? I am currently conducting research which seeks to establish that Charismatic Christianity, which started with Charles Parham in the early 20th century, has had the greatest influence on the church in America up into today. 

One possible piece of evidence for my case rests on the total population of Charismatic Christians in America. This number is difficult to discern though for a number of couple of reasons:


  Firstly, although there are denominations which represent Charismatic
  beliefs such as Assemblies of God, United Pentecostal Church
  International etc., these populations are not comprehensive in
  examining the totality of Charismatic influence; many
  non-denominational churches hold beliefs similar to Pentecostals for
  example.
  
  Secondly, virtually all Protestant denominations &amp; Catholicism have
  some influence of Charismatic Christianity in them
  today.
  The measure of this influence is difficult to quantify when
  determining how many Charismatic Christians are in actually in the
  population of Christians in America.




Given these difficulties listed, I am curious if any scholarly research group has conducted research to best piece together an estimate which best identifies the population of those which subscribe to the theology first promulgated by Charles Parham in the early 1900's.
Todd Johnson, who is the director of the Center for the Study of Global Christianity at Gordon Conwell Theological Seminary, reported on the global demographics of the Pentecostal and Charismatic renewal.

He does this by first breaking down our demographic of interest into a single group called “renewalists” which are comprised of three “waves”: Pentecostals, Charismatics, and neocharismatics. Despite the three waves, Johnson argues that they all point to an interconnected movement:


  “The case for the Pentecostal and Charismatic Renewal as a single
  interconnected movement can best be made by considering how the
  movement starts and spreads in any area, from the days of the earliest
  Pentecostals to those of current Charismatics and neocharismatics. The
  start of the movement anywhere has always been an unexpected or
  unpredictable happening rather than the result of any human planning
  or organization. First individuals (at random across the existing
  churches), then groups, then large numbers in semi-organized movements
  become filled with the Spirit and embark on the common Charismatic
  experience. All of them, originally, can collectively be termed
  Renewalists.”


Number of Renewalists in the United States

For these “renewalists,” as Johnson calls them, we find that they have quite a substantial representation in American Christianity. According to a reference Johnson makes to the World Christian Database, as of 2010, there are roughly 76,000,000 renewalists in the U.S.1 

That is to say approximately 1/3rd of all Christians in the U.S identify with renewalist ideology. This renewalist group makes up in fact the largest demographic of Christian in the U.S. today, with Catholics trailing in second at about 70,000,000 followers, or about 30% of the Christian population. 


Johnson, T.M. Soc (2009) 46: 479. The Global Demographics of the Pentecostal and Charismatic Renewal