A century ago, the overwhelming view of scholars was that Aramaic had entirely displaced Hebrew as a vernacular language well before the Roman conquest, probably around the Hellenistic Period of the 4th century BCE, or not long after.
However, these views have changed substantially in the 20th century, in large part due to archaeological indicating showing that Hebrew must have been widely understood and used for vernacular purposes in the 1st century CE.
I'll quote some relevant snippets from the excellent Wikipedia article on this:
In bold, I'm emphasizing opinions about when and where Hebrew survived longest as a vernacular language.
While there is no doubt that at a certain point, Hebrew was displaced as the everyday spoken language of most Jews, and that its chief successor in the Middle East was the closely related Aramaic language, then Greek, scholarly opinions on the exact dating of that shift have changed very much.
… The Qumran scrolls indicate that Hebrew texts were readily understandable to the average Israelite, and that the language had evolved since Biblical times as spoken languages do. Recent scholarship recognizes that reports of Jews speaking in Aramaic indicates a multilingual society, not necessarily the primary language spoken. Alongside Aramaic, Hebrew co-existed within Israel as a spoken language. Most scholars now date the demise of Hebrew as a spoken language to the end of the Roman Period, or about 200 CE.
The exact roles of Aramaic and Hebrew remain hotly debated. A trilingual scenario has been proposed for the land of Israel. Hebrew functioned as the local mother tongue with powerful ties to Israel's history, origins, and golden age and as the language of Israel's religion; Aramaic functioned as the international language with the rest of the Middle East; and eventually Greek functioned as another international language with the eastern areas of the Roman Empire. According to another summary, Greek was the language of government, Hebrew the language of prayer, study and religious texts, and Aramaic was the language of legal contracts and trade. There was also a geographic pattern: according to Spolsky, by the beginning of the Common Era, "Judeo-Aramaic was mainly used in Galilee in the north, Greek was concentrated in the former colonies and around governmental centers, and Hebrew monolingualism continued mainly in the southern villages of Judea." In other words, "in terms of dialect geography, at the time of the tannaim [1st and 2nd centuries CE] Palestine could be divided into the Aramaic-speaking regions of Galilee and Samaria and a smaller area, Judaea, in which Rabbinic Hebrew was used among the descendants of returning exiles." In addition, it has been surmised that Koine Greek was the primary vehicle of communication in coastal cities and among the upper class of Jerusalem, while Aramaic was prevalent in the lower class of Jerusalem, but not in the surrounding countryside. After the suppression of the Bar Kokhba revolt in the 2nd century CE, Judaeans were forced to disperse. Many relocated to Galilee, so most remaining native speakers of Hebrew at that last stage would have been found in the north.
In a 2006 paper, William Schniedewind concludes:
When we survey the use of Hebrew in the Persian, Hellenistic, and Roman periods, most scholars feel that spoken Hebrew did survive — at least in some isolated communities — as a vernacular language in Palestine until the second century A.D. (Fitzmyer 1970; Rabin 1976; Sáenz-Badillos 1993: 112–201; and Alexander 1999). Although there were major demographic changes in the Babylonian and Persian periods, a small number of villages and towns survived and presumably Hebrew would have continued to be spoken in such places. One expression of the
reassertions of Jewish autonomy in the fourth, third, and second centuries [BCE] would be the revival of Hebrew scribal institutions, which would have drawn on the continuation of a vernacular Hebrew as well as the deeply entrenched Persian scribal chancellery.
Still, the shift from Hebrew to Aramaic on every level was profound and irreversible. Hebrew was revived as a literary language reflecting the political and religious aspirations of Jewish groups in the Hellenistic period. Still, the shift from Hebrew toward Aramaic was not halted by the ebb and flow of Jewish autonomy in the Persian through Roman periods. By the third century AD, the language shift from Hebrew to Aramaic was complete and Hebrew had essentially disappeared as a vernacular language in Roman Palestine. Even while Hebrew language was receding as the vernacular and written language, it was being preserved as a liturgical language, a sacred tongue, and an icon of political legitimacy and national identity.
To summarize recent scholarship:
- Hebrew existed alongside Aramaic and Greek as a vernacular language in the 1st century CE.
- By this time, Aramaic and Greek dominated the coastal areas and the Galilee, and probably the upper classes of Jerusalem as well. Hebrew remained the vernacular language of rural southern Judea (the hilly agricultural region south of Jerusalem, including what is today the southern lobe of the West Bank).
- However, the last remaining native speakers of Hebrew probably lived in the north in the 2nd century CE, since many fled from Judea to Galilee after the Bar Kokhba revolt.