This series contains Ordnance Survey files documenting changes to public boundaries by statutory means. Each file relates to an area delimited by a poor law union boundary. These files commenced in the 1870s: each contains a reference or history sheet on which are entered each change, its effect on local government areas, and the statutory order that made the change. Poor Law Union Files were superseded in 1940 by a new series of County Files, although a few items were still being added until 1971. No system of Poor Law Union Files was ever introduced in Scotland.