Wikipedia gives a good summary:
“When the Christian Church came into being, polygamy was still practiced by the Jews. It is true that we find no references to it in the New Testament; and from this some have inferred that it must have fallen into disuse, and that at the time of our Lord the Jewish people had become monogamous. But the conclusion appears to be unwarranted.
Josephus in two places speaks of polygamy as a recognized institution: and Justin Martyr makes it a matter of reproach to Trypho that the Jewish teachers permitted a man to have several wives. Indeed when in 212 A.D. the lex Antoniana de civitate gave the rights of Roman Citizenship to great numbers of Jews, it was found necessary to tolerate polygamy among them, even though it was against Roman law for a citizen to have more than one wife.
In 285 A.D. a constitution of Diocletian and Maximian interdicted polygamy to all subjects of the empire without exception. But with the Jews, at least, the enactment failed of its effect; and in 393 A.D. a special law was issued by Theodosius to compel the Jews to relinquish this national custom. Even so they were not induced to conform.”
The International Standard Bible Encyclopedia adds:
Herod had nine wives at one time (Josephus, Ant, XVII, i, 2). Justin Martyr (Dial., 134AD, 141AD) reproaches Jews of his day with having “four or even five wives,” and for “marrying as many as they wish” (compare Talm). It was not definitely and formally forbidden among Jews until circa 1000 AD. It exists still among Jews in Moslem lands.
The following is from How Much Jewish Polygyny in Roman Palestine? (2001 – Adiel Schremer). Schremer first provides a helpful definition of what it means to be a polygynous society.
What precisely is meant when a given society is designated as polygynous? If one takes this term to mean that all, or even most, of the society’s male members marry more than one woman, it is evident that Jewish society of antiquity was not polygynous. However, such a definition would render it very difficult to find a polygynous society anywhere. For simple demographic reasons alone, it is very difficult to imagine the existence of a society in which every man marries more than one woman without assuming that this society also adopted certain mechanisms in order to control the distribution of the sexes so as to prevent an equivalent number of males and females…
A polygynous society is best defined as not monogamous, and a monogamous society is a society in which an enforced norm of monogamy exists.’ According to such a definition, a society which allows its male members to marry more than one woman and in which cases of polygyny are actually found – even if only limited cases – should be regarded polygynous. This classification does not reflect any statistical claim, nor does it contain any statement regarding the family life of most of that society’s members. Rather, it intends primarily to express something about the society’s attitude towards marriage and family life.
How common was polygyny in Jewish Roman Palestine? On the basis of the available sources no precise answer can be given to this question. To determine the exact percentage of men married to more than one woman at once is simply not possible, and so perhaps the answer to this question will never be known. However, it seems that the inability to provide an exact number is not the real issue. What is important, and particularly in light of the definition suggested at the beginning of this paper, is that Jewish society of Eretz Israel of the Second Temple, the Mishnaic, and Talmudic periods may be designated as a polygynous society. This conclusion is based, on the one hand, on the fact the rabbis did not prohibit polygyny, and, on the other, on the evidence indicating the actual practice of polygny during these periods.
Schremer, Adiel. “How Much Jewish Polygyny in Roman Palestine? (2001).” Proceedings of the American Academy for Jewish Research 64 (2001): 181–223. Print.
From the Jewish Encyclopedia:
The fact or condition of having more than one wife or husband at a time; usually, the practise of having a plurality of wives. While there is no evidence of a polyandrous state in primitive Jewish society, polygamy seems to have been a well-established institution, dating from the most ancient times and extending to comparatively modern days. The Law indeed regulated and limited this usage; and the Prophets and the scribes looked upon it with disfavor. Still all had to recognize its existence, and not until late was it completely abolished. At no time, however, was it practised so much among the Israelites as among other nations; and the tendency in Jewish social life was always toward Monogamy.
Polygamy was not offocially forbidden until the year 1000AD by Rabbi Gershom’s famous edict directed against Jews living in Europe. However there are efforts to overturn that ban by some Jewish rabbis and restore polygamy today:
An organization catering primarily to the Jewish Orthodox and ultra-Orthodox communities actively encourages and facilitates polygamy, claiming the practice will help reduce the number of single women within their communities and at the same time give Jews an edge in the demographic race against Arabs in Israel.