user: Question: When 31901 is the population what is the county?
Columns: ['Rank', 'City/Town', 'County', 'Region/Province', 'Population', 'Country']
Types: ['real', 'text', 'text', 'text', 'real', 'text']
Sample row: [1.0, 'Dublin', 'County Dublin', 'Leinster', 505739.0, 'Republic of Ireland']
SQL:

assistant: SELECT "County" FROM "Table" WHERE "Population" = 31901.0;