Utah became a territory on September 9, 1850 and the Territorial Legislative Assembly first met the following year on September 22, 1851. The Legislative Assembly was responsible for creating laws to govern the territory. These records contain the acts, bills, resolutions, memorials, and petitions of the first through thirty-first sessions (to statehood) of the Assembly. This series also contains reports, e.g. the Superintendent of Public Schools, University of Deseret; financial claims; and correspondence concerning the duties and actions of the Assembly. Within these documents charters of cities, divorce and marriage laws, laws regulating the physical construction of the state, legislation creating local governments, and numerous other laws setting the framework of life in Utah Territory can be found. The debate on polygamy can be witnessed through the bills and Governors' messages. Unfortunately, not all of the Governors' messages are contained in this series; for a more completeset see series 3145, JOURNALS.

The Legislative Assembly was divided into two houses, the House of Representatives and the Council. Representation was based on the population of counties or districts. A census was taken to determine the population of each county and district and then a vote was held. The governor appointed the members to the Council and House based on the election results. The House of Representative consisted of twenty-six members with a 1 year term. The Council had 13 members with 2 year terms. General elections were then held biennially on the first Monday in August (Laws of Utah 1851). In 1870, the terms of the House members were extended from one year to two (Laws of Utah 1871) and in 1880 the general elections were changed to Tuesday after the first Monday in November.

The Legislative sessions were held annually until 1870, usually in winter, from December to March. After 1870, biennial sessions were held in even numbered years until statehood. Some sessionrecords contain both bills and acts. The bills are the initial legislation and do not necessarily become law. Acts refer to bills that have passed both bodies and are signed by the governor. Engrossed bills refer to bills passed by both the Council and House. Some bills and acts contain the record of the proceedings for the legislation on the back of the bill. It will give a date and then state what happened on that date, e.g. "passed the house" or "sent to committee." In various sessions, only an oversized, formal copy of the official act can be found. Claims are those made to the state for money due an individual or group. Memorials are pleadings for federal action, usually made to the U. S. Congress. Resolutions are position statements which do not have the weight of law. Petitions are initiated by citizens desiring the introduction of particular legislation.