Which preposition to use with postoffices

in Occurrences 5%

BottomAmerican Army Postoffice in France on Mothers' Day, 1918.

with Occurrences 3%

There is a postoffice with a tower and a clock, a courthouse with a fountain and a cannon, a park with a bandstand and a baseball diamond, a townhall with a belfry and no bell, an exhaustive array of churches, the Imperial Hotel, and the market.

at Occurrences 2%

The postoffice at Brandon is over in the south wing where there are pigeon-holes and desks and such things.

departmentfor Occurrences 1%

It will be laid aside for a time while the nation discusses the political corruption of great cities; the scandalous conditions in Rhode Island; the evils attending reconstruction in the Philippines, and the scandals in the postoffice departmentfor none of which, by the way, is the Negro charged with any responsibility, and for none of which is the restriction of the suffrage a remedy seriously proposed.

on Occurrences 1%

On the site of the old postoffice on the corner of Wabasha and Fifth streets stood the Mansion house, a three-story frame building erected by Nicholas Pottgieser in early days at an expense of $12,000.

Which preposition to use with  postoffices