Paid county constabularies were first established by Peel's County Police Act of 1839, and were set up by the justices of the peace.
Montgomeryshire's was formed in 1840. Breconshire and Radnorshire did not have a police force until 1856-7, following the County and Borough Police Act, 1856, which required justices to establish forces where none existed.
See also Montgomeryshire: Journals of Thomas Jones, constable 1843-8 (M/SOC/7/42-44); correspondence and related papers relating to County Police force 1890-1931, miscellaneous files 1920-38 (MC/CSJ)
See also Radnorshire: Chief Constable's report and account 1889 (R/D/JGW/25)
Early records for the Constabulary in Breconshire, Montgomeryshire and Radnorshire may be found in the Quarter Sessions collections.