by Karl Kurtz
From the State House in Trenton, New Jersey there is a clear view across the Delaware River into Pennsylvania. In the Google Earth image below, the complex of buildings below the "A" pin marker at the top right is the State House and the white line in the middle of the river at the lower level is the Pennsylvania border.
David April, the tour program coordinator for the New Jersey Legislature, wonders if his is the only state capitol from which one can see another state.
After some investigation, the only other capitol from which another state is visible that we know of for sure is Cheyenne, Wyoming. The Colorado border is only about 10 miles south of the Wyoming Capitol in Cheyenne, and one can see mountain peaks in the Centennial State from the Capitol.
Massachusetts is also just a few miles away from the State House in Providence, Rhode Island. Paula Dominguez, research director for the Rhode Island General Assembly, says that she lives in Rhode Island but has to drive through Massachusetts to get to the State House. But she says that the city of East Providence blocks the view from the capitol to the Bay State. Another friend in Providence reports, "On a clear day from the rim at almost the top of our dome (where no one is supposed to go, but some do), you possibly could be able to see across the bay toward the MA South Shore. I cannot say that I have seen that far, however."
Annapolis, Baton Rouge and Tallahassee are each about 30-40 miles from another state's border (Delaware, Mississippi and Georgia, respectively), but it seems unlikely that one can see that far from those capitols.
Corrections to this post are welcome! (See comments below.)