During the 16 weeks between Lincoln's victory in the 1860 presidential election and Inauguration Day, seven slave states had declared their secession from the Union and formed the Confederate States of America. Specifically Alabama, Florida, Georgia, Louisiana, Mississippi, South Carolina and Texas. Nearly all of the members of Congress from each of these states at this time (35th Congress) were Democrats. So yes, you can say democrats boycotted Lincoln's inauguration in a major way.