The sacristy is usually located inside the church, but in some cases it is an annex or separate building (as in some monasteries). In most older churches the sacristy is near one of the side altars or more usually behind or to the side of the main altar. In newer churches the sacristy is often in another location, such as near the entrances to the church. Some churches have more than one sacristy, each of which will have a specific function. Often additional sacristies are used for maintaining the church and its items - such as candles and other materials.
The sacristy is also where the priest and attendants vest and prepare before the service. They will return there at the end of the service to remove their vestments and put away any of the vessels used during the service. The hangings and altar linens are stored there as well. The Parish registers may be kept in the sacristy and are administered by the parish clerk.
Sacristies usually contain a special wash basin, called a sacrarium, in which the drain flows directly into the ground to prevent sacred items such as used baptismal water from being washed into the sewers or septic tanks. The sacrarium is used to wash linens used during the celebration of the Mass and purificators used during Holy Communion. The cruets, chalice, ciborium, paten, altar linens and sometimes the Holy Oils are kept inside the sacristy. Sacristies are usually off limits to the general public. The word "sacristy" derives from the Latin sacristia, sometimes spelled sacrastia.
A person in charge of the sacristy and its contents is called a sacrist or a sacristan. The latter name was formerly given to the sexton of a parish church, where he would have cared for these things, the fabric of the building and the grounds.