Immigrant and migrant farmworkers from Mexico and other countries are large and growing in number and in importance to U.S. agriculture, but they often are not counted in the decennial census due to high mobility, illegal status, and/or unconventional housing. This report is based on ethnographic research conducted in California’s Santa Maria Valley, an active agricultural area rich in labor-intensive cultivation of prime vegetable and fruit crops. It is based on comprehensive interviews with immigrant and migrant agricultural workers concerning their migratory and employment histories, housing arrangements, and relationships to Mexican communities. The report concludes that routine census procedures can only result in a significant under-reporting of numbers of immigrant and, particularly, migrant farm workers in Santa Maria and, by extension, in other regions of the country which rely heavily upon imported labor; that many immigrant and migrant farmworkers have good reason to fear exposure to government representatives and thus will attempt to remain hidden from them; and that lack of adequate housing contributes to difficulties in locating and enumerating this population. More accurate enumeration and description of this population can be accomplished if bilingual and bicultural  ensus workers are trained to patiently and repeatedly approach their households and unconventional dwellings using ethnographic research methods.