Here are a few tips to keep in mind while searching for Puerto Rican ancestors.
Puerto Rico became a US Territory in 1898 as a result of the Spanish-American War. US Armed Forces began inhabiting the island during this period and you can find these service members listed in the 1900 US census.
In 1910, all residents of Puerto Rico began appearing in the US Census and you can find these records in Ancestry, HeritageQuest or FamilySearch. Keep in mind that Puerto Rican census records will be in Spanish.
Puerto Ricans born on or after April 25, 1898 were granted US Citizenship in 1917. Puerto Ricans born before 1898 may have naturalized and those records would be available at NARA.
The Spanish government in some Puerto Rican municipalities kept civil registrations of births, marriages, and deaths. Civil registration for the entire territory began in 1885 and these records contain a lot of important genealogical information. You can find Puerto Rican civil registration collections on Ancestry and FamilySearch.
When researching vital records before 1885, use Catholic Church records. FamilySearch has a collection of Puerto Rican Catholic Church records dating back to 1645.
For more information on Puerto Rican genealogy, visit the FamilySearch Research Wiki or watch one of FamilySearch's free webinars.