New Mexico Population for Largest Counties
            1900 to 1920 by decades
                    US Census Data

County        1900      Rank       1910         1920       Rank         Percent
                                                                                           Increase
Bernallilo     28,630       1        23,606       29,885          1        + 4.3
Dona Ana    10,187      -          12,893       16,548           5      +62
Grant          12,887       5         14,813       21,939           3      +70
Rio Arriba     13,777      4         16,624       19,552           4       +42
San Miguel       22,053       2         22,930       22,867           2        + 3.7
Santa Fe        14,770      3         14,658       15,030           -         + 1.8

This table illustrates well the results of the Territorial Bureau of Immigration. They produced and distributed illustrated books, booklets, and pamphlets trying to dispel the idea of desolation, aridness, of the Territory and to emphasize economic opportunities. The Bureau’s sole goal was to promote immigration from the east to the territory. The increase in Grant County was most likely because of mining. San Miguel remained stable after the railroad boom of the 1800’as did Bernallilo. Rio Arriba showed a significant increase, I would guess because of agriculture and livestock production. Dona Ana probably came from growth in the Collage and agriculture through irrigation. And the table shows why city fathers in Santa Fe worried over the city decline and the resulting push to remake the city to attract tourism.
During the twenty year period additional counties were formed by dividing existing counties. The only one affected in this list is Bernalillo. Torrance county was formed n 1903 by taking parts of Bernalillo and Valencia county. Also Sandoval County was formed from part of Bernalillo County in 1903. This skewed the population a bit.