28mm County Marshall's Office

I'm 100% sure it should not say county Marshal either. Though it can be spelled with two 'L's and be correct (Webster's Encyclopedic Unabridged Dictionary of the English Language. New York: Gramercy Books. 1996.)

From Wikipedia:
American Old West (for example, Arizona Territory and Texas of the 1880s): Marshals, usually called town marshals or city marshals (since the larger cities were often punctilious about their titles), were appointed or elected police officers of small communities, with powers and duties similar to those of a police chief; these powers generally ended at the border of the community. By contrast, federal marshals (U.S. marshals) worked in a larger territory, especially in pioneer country, and this area could potentially overlap with the state or territorial office of county sheriff (who then, as now, policed communities, as well as areas between communities). The word marshal is still used in this sense, especially in the American Southwest. (See List of Western lawmen.) Town or city marshal is still the name for the head officer of some community police forces.