The immigration act of 1924 was enacted May 26, 1924, and signed by...
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Here is how this immigration act changed immigration: 
HeinOnline -- 43 Stat. 153 1918-1925
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There are quota and non-quota immigrants. Certain countries (like other countries in the Americas) had no limit on the number of immigrants from their country.
Here is how this immigration act changed immigration: 
The preference "shall not apply to immigrants of any nationality the annual quota for which is less than 300". So if you are a skilled agricultural worker or the immigrant child of a US citizen but from an unfavorable country, your immigration will not be given "preference".
This quota limited the annual number of immigrants who could be admitted from any country to 2% of the number of people from that country who were already living in the United States as of the 1890 census. This is a reduction down from the 3% cap set by the Emergency Quota Act of 1921, which used the Census of 1910. They used the 1890 census as a reference point to further restrict immigration of Southern Europeans and Eastern Europeans (in 1890, fewer Italians and Bulgarians lived in the U.S than in 1910) and to encourage the immigration of people from Britain, Ireland, and Northern Europe.
Immigrants from the Americas are counted as "Non-Quota Immigrants".
People can claim to be "non-quota immigrants" but must have facts to base the claim. Also, in addition to showing criminal record, must show mental health record of parents.
The immigration act of 1924 was enacted May 26, 1924, and signed by President Coolidge. It was the first immigration act to set a permanent numerical limit on immigration. Total annual immigration was capped at 150,000 individuals. The ultimate goal of the immigration act according to the U.S. Department of State Office of the Historian was "to preserve the ideal of American homogeneity" and preserve racial homogeneity. Despite this aim, there was no limit on immigration from other countries in the Americas. The law severely restricted the immigration of Africans and banned the immigration of Arabs and Asians. It also restricted immigration of Southern Europeans and Eastern Europeans (especially Italians and Eastern European Jews).