(CNN) -- A polygamist sect member arrested following last year's raid of a west Texas ranch was sentenced Tuesday to 10 years in prison for sexually assaulting an underage girl, authorities said.
Raymond Jessop was found guilty last week of assaulting a girl under 17, with whom he had entered into a "spiritual" marriage, said Jerry Strickland, a spokesman for the state attorney general.
Jessop also received an $8,000 fine, said Sheriff David Doran, of Schleicher County, Texas.
The victim in the case was one of 400 children seized from the Yearning for Zion Ranch in Eldorado, Texas, in April 2008 by state child welfare workers. The children were returned after the Texas Supreme Court ruled that the state had no right to remove them and lacked evidence to show that they were in danger of abuse.
Jessop belongs to the Fundamentalist Church of Jesus Christ of Latter-day Saints. The church -- a 10,000-member offshoot of the mainstream Mormon church -- openly practices polygamy on the ranch, as well as in Arizona and Utah.
Critics of the sect say young girls are forced into "spiritual" marriages with older men and are sexually abused. Sect members have denied any sexual abuse.
CNN's Dave Alsup contributed to this report.