Northumberland County was created in 1785.
Here are some of the parishes of Northumberland co. and the year they were established

Newcastle 1786
Alnwick 1786
Glenelg 1814
Chatham 1814
Nelson 1814
Ludlow 1814
Northesk 1814
Blissfield 1830
Blackville 1830
Hardwicke 1851
Derby 1859
Southesk 1879
Rogersville 1881