The Fourth Wisconsin Legislature convened in regular session from January 8, 1851, to March 17, 1851. Senators representing odd-numbered districts were newly elected for this session and served the first year of a two-year term. Assembly members were elected to a one-year term. Assembly members and odd-numbered senators were elected in the general election on November 5, 1850. Senators representing even-numbered districts were serving the second year of their two-year term, having been elected in the general election held on November 6, 1849.^[1]

• January 20, 1851: The Wisconsin Legislature, in joint session, re-elected Henry Dodge to a six-year term as United States Senator.^[2]
• November 4, 1851: Leonard J. Farwell elected Governor of Wisconsin.

• January 22, 1851: Joint resolution in relation to the Honorable Isaac P. Walker, 1851 Joint Resolution 1
• February 1, 1851: Act to incorporate the Fire Department of the City of Milwaukee, 1851 Act 26
• February 4, 1851: Act providing for the election of a Chief Justice, 1851 Act 39
• February 6, 1851: Act to set apart and incorporate the County of Oconto, 1851 Act 44
• February 11, 1851: Act to set apart and incorporate Door County, 1851 Act 66
• February 15, 1851: Act to set apart and incorporate the County of Waushara, 1851 Act 77
• February 17, 1851: Act to incorporate the County of Waupaca, 1851 Act 78
• February 17, 1851: Act to divide the county of Brown and create the county of Outagamie, 1851 Act 83
• March 10, 1851: Act to prevent the killing of deer in certain months of the year, 1851 Act 171
• March 11, 1851: Act to change the name of the town of "Pike" in Kenosha county to "Somers," 1851 Act 211

• 1st Regular session: January 8, 1851–March 17, 1851