While including churches in other regions of the United States, it also has congregations in Mexico, Central America, and the Caribbean.

The churches of the Lancaster Mennonite Conference (LMC) make up 24 districts including: Bowmansville-Reading, Elizabethtown, Ephrata, Groffdale, Harrisburg, Juniata, Lancaster, Landisville, Lebanon, Lititz, Manheim, Manor, Martindale, Mellinger, Millwood, New Danville, New York City, North Penn, Pequea Valley, Philadelphia, Washington-Baltimore, Weaverland-Northeast Pennsylvania, Williamsport-Milton, Willow Street-Strasburg, and York-Adams Districts.

In 1725, five representatives, Martin Baer, Hans Burkholtzer, Christian Herr, Benedikt Hirsche, and Johannes Bowman, attended the first general Mennonite Conference when the Dordrecht Confession was translated into English.

They overflowed into what are now neighboring counties and established daughter colonies in Maryland, Virginia, New York, Canada, and Ohio.

Differences over issues related to divorce and remarriage, television, and relaxed dress requirements resulted in the formation of the Eastern Pennsylvania Mennonite Church in 1969.

Two hundred members left in 1975 to form the Conservative Mennonite Churches of York and Adams Counties, Pennsylvania.

[7] On November 19, 2015, citing a "cultural and theological divide" over MC USA's increasing support for same-sex marriage and LGBTQ relationships, a proposal by the Board of Bishops to leave MC USA was ratified by 82.3% of those voting.