Selecting Counties in ArcGIS

Hi.
I am new to ArcGIS and have mapped locations of structures in a state into ArcMap 10.2.1. The locations were in an MS Access table, which I imported into ArcMap. I would like to run analysis of other table attributes of the structures by counties. However, I do not know how to make ArcMap classify the structures by counties. (The locations were imported using longitude and latitude data points.) Does this question make sense? I hope so. Please help!