One specific route passing through the county seats of the same named county

[roadman65]

I found it interesting that US 9 passes through both Newark, NJ and Elizabethtown, NY which are not only county seats of their respected counties, but of the same county of the same name.

Are there any other such occurrences?

[algorerhythms]

This is an almost occurrence: US 220 passes through Cumberland, Maryland (seat of Allegany County) and Covington, VA (seat of Alleghany County).

[dfwmapper]

Guessing there are many. First one I found was US 34 passing through Corning, IA, and Hastings, NE, which are both seats of Adams County.

https://en.wikipedia.org/wiki/Category:United_States_county_disambiguation_pages is a good place to start looking for counties of the same name.

[Thing 342]

US 60 passes through Amherst, Buckingham, Cumberland, and Powhatan, all seats of their namesake counties.

[dfwmapper]

US 60 passes through Amherst, Buckingham, Cumberland, and Powhatan, all seats of their namesake counties.

The question was counties of the same name in different states (Essex County, NJ, and Essex County, NY, in the example), not counties where the county seat has the same name as the county.

[WNYroadgeek]

NY/PA 5 enter both Erie and Buffalo, the county seats of each state's respective Erie County.

[pianocello]

US 54 goes through Bowling Green, MO and Pittsfield, IL, both of which are seats of Pike County.

[DandyDan]

US 30 goes through (or at least around) Marshalltown, Iowa and Plymouth, Indiana, both of which are county seats for Marshall County.  It also goes through North Platte, Nebraska and Kemmerer, Wyoming, which are both the seats of Lincoln County.

[jp the roadgeek]

US 202 has an interesting one: It passes through Westchester County, NY, and the city of West Chester, PA, which is in Chester County.

US 1 passes through 3 different Middlesex Counties (NJ, CT, MA). It passes through the county seat in NJ (New Brunswick), barely misses MA (Cambridge), and CT doesn't have county seats.

[Scott5114]

US-66 went through Springfield MO and Springfield IL, seats of Greene and Sangamon counties, respectively.

[roadman65]

I completely forgot this one.  US 1 passes through both Augusta, GA and Rockingham, NC which both are county seats of Richmond County.

[bassoon1986]

An almost. US 65 goes through the seats of East Carroll Parish in LA and Carroll County in MO

[pianocello]

I completely forgot this one.  US 1 passes through both Augusta, GA and Rockingham, NC which both are county seats of Richmond County.

Bonus points: it also goes through Richmond, VA, which is an independent city. It doesn't go through the seat of Richmond County, VA, though.

[sandwalk]

Close but not quite:

Interstate 90 passes through Erie County OH, Erie County PA, and Erie County NY.  However, I-90 is just a few miles outside of each county's county seat (Sandusky OH, Erie PA, and Buffalo NY).

[NWI_Irish96]

I-64 passes through Mount Vernon, Jefferson, IL and Louisville, Jefferson, KY
I-65 and US 31 both pass through Louisville, Jefferson, KY and Birmingham, Jefferson, AL
US 40 passes through Marshall, Clark, IL and Springfield, Clark, OH
US 40 passes through Washington, Washington, PA and Hagerstown, Washington, MD

[golden eagle]

US 82 passes through Winona, MS; and Montgomery, AL, both which are in Montgomery County.

[codyg1985]

US 43 passes through Mobile, (just barely), Tuscaloosa, and Fayette Counties with county seats of the same name. There is also Lawrence County/Lawrenceburg, TN that US 43 passes through, but technically that's not the same. Mobile just barely counts since US 43 was truncated.