The difference can change where a child lives, who makes major decisions, and even how expenses, child support, and court outcomes are handled. After a divorce or separation, parents may share one kind of custody but not the other, so the label affects day-to-day life as much as the legal paperwork.

Physical custody means where the child lives and which parent handles routine daily care. It may be sole or shared, and a schedule can range from primary residence with one parent to roughly equal time. Legal custody means the authority to make major decisions for the child, such as choices about school, medical care, religion, and activities. Parents can share legal custody even if one parent has most of the physical custody, or one parent can have sole decision-making authority.

In practice, the distinction matters when parents disagree about medical treatment after a crash, counseling, or changing schools after a move. It can also affect who has standing to act quickly for a child and how a judge evaluates the child's best interests.

In Illinois, courts no longer usually use the old custody labels. Under the Illinois Marriage and Dissolution of Marriage Act, updated in 2016, the law speaks in terms of parenting time and allocation of parental responsibilities. Older orders and everyday conversation still use "physical" and "legal" custody, but Illinois courts focus on those newer categories.