Why is Election Day held on Tuesday after the first Monday in November?

 For much of our history, America was a predominantly agrarian society. Law makers therefore took into account that November was perhaps the most convenient month for farmers and rural workers to be able to travel to the polls.

Since most residents of rural America had to travel a significant distance to the county seat in order to vote, Monday was not considered reasonable since many people would need to begin travel on Sunday. This would have conflicted with Church services and Sunday worship. Tuesday, would also not conflict with market day, which was on Wednesday in many towns.   

Lawmakers wanted to prevent Election Day from falling on the first of November for two reasons. First, November 1st is All Saints Day, a Holy Day of Obligation for Roman Catholics. Second, most merchants were in the habit of doing their books from the preceding month on the 1^st and Congress did not want the economic success or failure of the previous month to influence the outcome of the election.

Source: http://www.infoplease.com/spot/electionday1.html