I had studied the law and removed to Springfield to practice it. 
- Abraham Lincoln

While running for the Illinois legislature in 1834, Lincoln met John Todd Stuart, a fellow Whig also running for office, who loaned Lincoln some law books.  Lincoln studied enthusiastically.  He got his law license in September 1836 without attending law school or passing the bar as it is known now.  Instead, he was declared to have a “good moral character” and was examined by the Illinois Supreme Court.  The Court issued Lincoln a license to practice law in any state court in Illinois.  He came to Springfield to work with John Todd Stuart in April 1837.  Four years later, Lincoln became junior partner to Stephen Trigg Logan.  By 1844 he was the senior partner with William Herndon.
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Lincoln rapidly gained respect and fame for his courtroom skills. Law offices around the town square often saw law clerks gathered around listening to Lincoln’s stories. It was a skill that stood him in good stead in front of a judge.  Lincoln handled a variety of cases, including several as a de-facto corporate lawyer for the Illinois Central Railroad. This work once earned the Lincoln-Herndon partnership $5,000 in legal fees.  Lincoln handled disputes over property, divorces, even murder.  One case had Lincoln on the master's side in a fugitive slave case but another had him defending a free black man from being declared a fugitive slave.  Lincoln won and lost cases, some went to the Illinois Supreme Court.  Several cases affected Illinois Constitutional law, but most cases covered debt collection and contracting. 

Lincoln also maintained a practice in the federal courts where he represented as many out-of-state clients as Illinois residents including one case between transportation companies in St. Louis and Chicago that helped establish railroad prominence in the state.  He even argued one case at the U.S. Supreme Court while he was in Washington serving as a congressman, and was an attorney-of-record for four more.  Most of his legal fees, which he split evenly with his partner, averaged $15-20 per case, but Lincoln was considered very successful. Current scholarship shows that he was involved in at least 5,173 cases in his 24-year career.  Studies of his legal work are still on-going 150 years after he stopped practicing (see www.thepapersofabrahamlincoln.org). 

Lincoln “rode the Illinois circuit.”  As the state was rural and sparsely populated, most counties did not have a full-time judge.  He was one of the lawyers and judges who came to town twice a year to try cases.  Lincoln worked on the 8th Judicial Circuit.  It covered 14 counties and 10,000 square miles, an area roughly the size of Maryland.  Although he was away from home for three months at a time on these circuit trips, he enjoyed the time with colleagues.  He also used the time to politick for the Whig party and even took the stump for himself once in a while.

Lincoln’s legal knowledge stood him in good stead during the presidency.  To bring about the end of slavery, he made sure that the Emancipation Proclamation of 1862 contained the strongest legal text possible.  His past skills in persuading juries were put to the test to convince his skeptical cabinet that it was even possible for the President to issue the document.  Some have argued that it did not free a single slave.  However, Lincoln insisted on issuing it although he admitted it “had no constitutional or legal justification, except as a military measure.”  But the proclamation started the legal process to fulfill his wish that “all men every where could be free.”  It became the most important document of his presidency.