Place data by county on the Census web page

From a self-described Census geek:

Places within County (or Town)

The Census Bureau uses a three digit Summary Level as a way to identify a certain level of geography. A few Summary Levels to remember are:
040 – State
050 – County
060 – Subcounty (City/Town in NY)
070 – Place/Reminder (or part)

These summary levels are very hierarchical and make up the higher level. So all counties make a state, all subcounties make a county, and all level 070 make up a subcounty. If a place is split by two towns, this place will have two records at level 070, one for each town. The city of Geneva is the only city with two 060 records (one in Ontario and one in Seneca County).

There are some additional summary levels related to places tabulated in AFF and things get very complicated:
155 – County (or part) with Place
159 – Place (or part) with County
160 – Place with State
To see summary levels in AFF you have to go to the Name tab, collapse the Geographic Type in the Filter Options and expand the Summary Level. Level 155 and 159 are normally hidden from view, but shown when you select All Summary Levels in the grey bar above the results.

If you select level 155 you can narrow your results and select Within State and Within County. You end up with a list of places and part of places that are within each County. If a place crosses county boundaries this summary level will give you the results for the part!

Summary level 159 works similar, but instead of a list of counties to select from, you get a list of places and counties to select from. This is not very handy and results are identical to level 155.
Level 160 is a collection of records for places as places do not cross State boundaries. This level is very much equivalent to selecting “City or Town” from the Geographic Type and the places returned using the method Dale described as per Bob’s suggestion returns places with this Summary Level.

So if you want data on the complete places (villages, CDP’s and Cities) that are fully or partially within a county, use level 160. If you are interested in the parts that are within a county use level 155 and if you want to split the places by towns, use level 070.

The Estimates Universe is comparable, but slightly different as it does not contains CDP’s (CDP = Census Designated Places). The Census Bureau assigned a different set of summary levels to this universe. Instead of level 160, 155 and 070, places can be found using Summary levels 162, 157 and 071. That is if the sub county estimates were available using AFF. At the moment these estimates are only available in downloadable format.