Is local government always better?

I used to think so, and while I haven't changed my mind, I am wondering...

(a)  What if you took into account monitoring and reporting of government activities by interest groups?  The primary bulwark against corruption.  Suppose you have a federal government charged with detecting and curbing environmental pollution.  This is one branch of government who must coordinate its efforts across a vast collection of regions, political districts, and people.  However, it is relatively easy for environmental interest groups (and, say, libertarian groups concerned that the power to mitigate pollution is being abused) to hone in on this one organization and criticize it brutally in the public arena.
     Now suppose each U.S. county is charged with detecting and curbing environmental pollution.  Wouldn't it be hard for interest groups to observe the tens of thousands of government agencies, and wouldn't it be impossible for an interest group to form in each U.S. county?  Wouldn't the county-level agencies be easier to corrupt?
(b)  Now let me ask you whether local or federal government is more inclined towards corruption?  What is your impression?  Can the wealthy and corrupt better control a city council, or a federal agency?
(c)  One final question: take examples of undeniable political corruption in the U.S., and ask yourself whether that power was wielded at the local or national level?  There is only one person in the U.S. I believe was a de facto dictator: Huey Long, in Louisiana (as portrayed by the character Willie Starks in the movie All The King's Men).  This guy exploited the pauperism of Louisiana citizens during the Great Depression and had almost the entire state in his hands.  Nothing of the sort has emerged at the national level, that I know of, at least.  Certainly, if FDR could have acquired Long's power, he would have.  But he was watched and attacked by too many people to be so corrupt.

Just a thought...