For US and most state Distict Courts - there is no set number of judges assigned. There is a sufficient number assigned to hear the caseload of that paricular court but since they all hear cases...
A judge is assigned to particular branch (either civil or criminal) of the District Court to which they are assigned. Normally they rotate every so often but at the direction of the Chief Judge of...
According to the 2009 Annual Report of the Director for Judicial Business of the US Courts, there are 678 authorized seats for judges in the US District Courts; there are also an addition 523...