Because of its Spanish heritage, Texas originally was entirely Roman Catholic except for unconverted Indians. Consequently, the early history of Texas is almost identical with that of the Roman Catholic Church in the area. Under the Mexican Republic, the Catholic Church continued as the sole recognized religious body. In order to receive the generous land grants given by the Mexicans, Anglo-American immigrants had to sign a paper saying that they followed the Catholic religion. With an average grant of 4,605 acres (1,864 hectares) as bait, many early Protestants and atheists must have felt little hesitancy about becoming instant Catholics.

The Mexican government was careless about enforcing adherence to the Catholic faith in Texas, however, and many Baptists, Methodists, and Presbyterians drifted in from the east. The Methodist practice of having itinerant ministers range over frontier areas was particularly well suited to the Texas scene and, in 1837, the church hierarchy sent three preachers to the new republic. The first presbytery had been formed by that date and Baptists had organized in Houston by 1840. Swedish and German immigrants brought their Lutheranism with them; the first German Lutheran synod was organized in Houston in 1851.

Geographically, Texas tends to be heavily Protestant in the north and east and Catholic in the south and southwest. Leading Protestant denominations and their known adherents in 2000 were the Southern Baptist Convention, 3,519,459; the United Methodist Church, 1,022,342; Churches of Christ, 377,264; Assemblies of God, 228,098; the Presbyterian Church USA, 180,315; the Episcopal Church, 177,910; Independent Charismatic Churches, 159,449; the Church of Jesus Christ of Latter-Day Saints, 155,451; the Evangelical Lutheran Church in America, 155,019; Independent Non-Charismatic Churches, 145,249; and the Lutheran Church—Missouri Synod, 140,106. Roman Catholics numbered 4,368,969 in 2000. There were an estimated 128,000 Jews, 114,999 Muslims, and about 10,777 adherents to the Baha'i faith. There were about 9.2 million people (44.5% of the population) who were not counted as members of any religious organization.