He and Harold, as well as their other friend Philip Westbourne, after years of walking through the Rockies, decided that they are searching for a suitable area near the Pacific Northwest, and they finally did. Later on, they founded out that the area, near the Pacific Northwest (most likely coastal Oregon), was a sacrificial site of native American importance. Their bundling neighbours decided to build a town around that area, even though Philip called that 'Grizzly Hill', because of the grizzly bears that lived there. Ta da! They built the oldest part of the Simpsons' hometown anyway.
But as Grizzly Hill grew faster than Port Charles (but still slowly) to include the first Burns family mansion and a milling plant, Harold left due to his disappointment, so he has to find an area south of the Grizzly Hill town, and he eventually did find it. As it turns out, the area was a prairie grassland - a highly important one to conserve! So he has to conserve much of it in order for his fellow neighbours to build a town around it. They called it 'Mudhole Heights', due to the marshy terrain.
Harold Shelbyville married a single neighbour of his named Rachel Thompson. Although imperfect as a couple, they pretty much lived a lot more happily than the parents of Johannes Springfield ever did. They adopted two orphans named Tommy and Teagan, both of whom were fraternal twins and lived fairly longer than the adoptive parents themselves.
Rachel and Harold died on August 14th 1827 of tuberculosis. Both were seventy seven years old.