In 1820 he accompanied Governor Cass, as Secretary, in his expedition to the sources of the Mississippi, travelling a distance of over four thousand miles through the Indian Country in a birch-bark canoe, from the 20th of May to the 20th of November. In this year he revised the laws of the Territory, which were published by the authority of the Legislature. In 1821 he was admitted an attorney of the Supreme Court of the United States at Washington. In 1823 the country north of lakes Huron and Michigan, and west of lakes Michigan and Superior, was made by Congress a judicial district, and he was appointed by James Monroe its Judge, with the title of "an additional Judge of the Territory of Michigan." He performed the duties of this office until the year 1832,--having married, and fixed his residence at Green Bay, then the largest settlement in the country north or west of Detroit. In 1832 he was appointed by the Secretary of War a Commissioner to locate Military Roads from Fort Howard, at Green Bay, to Fort Crawford on Prairie du Chien, and to Fort Dearborn at the mouth of Chicago Creek, now the site of the city of Chicago,--between which points there were then scarcely twenty white inhabitants. In 1834 and 1835 he served in the Legislative Council of Michigan, having been elected by the voters west of the Lake; and introduced the measure of a State government, which was adopted by the Council. He contended for the right of the people to form a government for themselves, under the provisions of the Ordinance of 1787. By this measure a territorial government was obtained for Wisconsin, and a permanent separation from Michigan of the country west of Lake Michigan, which had been attached to that Territory in 1818, when Illinois was admitted into the Union. It had been sought in vain of Congress from the year 1825,--the application having been successfully opposed by the party averse to laying the foundation of new non-slaveholding States. In 1837 he was elected Delegate to Congress from Wisconsin, and continued to serve in that office by reëlection until the year 1841, when he was appointed Governor and Superintendent of Indian Affairs in that Territory; and as Commissioner held treaties at Oeyoowurah, on Minnesota River, with the Dakotahs, and with the bands of that nation on the Mississippi River. It was in 1837 that he laid out the town of Madison, and succeeded in making it the seat of government,--one of the most valuable services which he ever rendered that State. It is now considered one of the most beautiful sites for a town. When selected by him there was not a white settler within forty miles, and it was occupied by Winnebago Indians. He was elected and served as a member of the Convention to form a State Constitution in 1846 for Wisconsin.