Bill's mother, Lois Henrickson, is a descendant of the founding family of Juniper Creek, the polygamy sect where Bill was born and raised. She married Bill's father, Frank Harlow, over 40 years ago, becoming the second of his five wives, and the two have had three kids together: Bill, his younger brother Joey, and a daughter Maggie who died over 20 years ago. Following rules common to some sects, the children were all given their mother's last name.
As granddaughter of Alder Henrickson, the founder of Juniper Creek, and daughter of Orville Henrickson, past prophet of the sect, Lois grew up as compound elite. When Roman Grant assumed the role of prophet in a kind of coup, Lois felt dispossessed and marginalized and became spiteful. As much as she's developed an independent streak, she's still quick to enlist Bill to straighten out family troubles.