The U.S. Census Bureau gives the population of Trinidad, California as follows:
| Year | 1990 | 2000 | 2010 |
| Count | 362 | 311 | 367 |
The counts above pertain only to residents within the official Trinidad City Limits:
Trinidad City Limits
Many more with Trinidad, CA 95570 mailing addresses reside outside of the City Limits. As of this writing (May 10, 2011) the Census Bureau had not yet released a 2010 Census count for ZIP code 95570, but in the 2000 Census, 2,352 people lived in the ZIP code tabulation area. The 95570 ZIP includes the City of Trinidad plus unincorporated coastal neighborhoods from just north of Humboldt Lagoons State Park to Crannell: