1931 Census of England and Wales, General Report, Table 84 : " Welsh Speaking Population, Proportion per 1,000 Persons Aged Three Years and Over in Counties, County Boroughs and Urban Areas with more than 50,000 Population".

  Total Welsh Speaking Welsh only Both English and Welsh
1931 1921 1931 1921 1931 1921
WALES AND MONMOUTH 368 371 40 63 328 308
Counties:            
  Anglesey 874 849 239 310 635 539
  Cardigan 871 821 200 261 671 560
  Merioneth 861 821 221 297 640 524
  Carmarthen 823 824 92 165 731 659
  Caernarvon 792 750 214 262 578 488
  Denhigh 485 484 54 85 431 399
  Montgomery 407 423 68 89 339 334
  Brecknock 373 372 20 45 353 327
  Flint 317 327 10 23 307 304
  Pembroke 306 303 40 58 266 245
  Glamorgan 305 316 8 22 297 294
  Monmouth 60 64 1 2 59 62
  Radnor 47 63 0 5 47 58
Large Towns:            
  Rhondda Urban District 465 455 11 30 454 425
  Merthyr Tydfil County Borough 398 414 9 23 389 391
  Swansea County Borough 273 285 5 17 268 268
  Cardiff County Borough 51 50 1 3 50 47
  Newport County Borough 21 21 0 0 21 21