Take a look at the l10n_uk module.  This module imports a CSV file to populate UK Counties.

https://github.com/odoo/odoo/tree/10.0/addons/l10n_uk

You can see in the __manifest__ file of the module the direction to import the file:

'data': [ 
   'data/res.country.state.csv',
],

Also at https://github.com/odoo/odoo/blob/10.0/addons/l10n_uk/__manifest__.py#L26

The CSV file looks like this:

"id","country_id:id","code","name"

"state_uk_1","base.uk","A1","Aberdeenshire"

"state_uk_2","base.uk","A5","Angus"

"state_uk_3","base.uk","A7","Argyll"

"state_uk_4","base.uk","A9","Avon"

"state_uk_5","base.uk","B1","Ayrshire"

"state_uk_6","base.uk","B3","Banffshire"

"state_uk_7","base.uk","B5","Bedfordshire"

"state_uk_8","base.uk","B7","Berkshire"

"state_uk_9","base.uk","B9","Berwickshire"

"state_uk_10","base.uk","C1","Buckinghamshire"

"state_uk_11","base.uk","C3","Caithness"

Also at https://github.com/odoo/odoo/blob/10.0/addons/l10n_uk/data/res.country.state.csv

Which imports these records into Odoo:

Also, see:

https://www.odoo.com/documentation/10.0/reference/data.html#csv-data-files