In my area, most of the towns were started in the 1850's. Searching under sidewalks, especially those in front of buildings is where you will find the coins from the 1850's. When I search a place like that you are not likely to find coins newer than 1900. Many times I have found coins older than the town itself. If conditions are right you will find more Seated Liberty coins than Barbers. I have even found a couple of Bust coins that were dated 30 years before the town was started.
Another place to find older coins are in rural churches and schoolhouses. Preferably if the church or school is gone. I have an 1874 atlas of of each county in the state. It shows were all the schools and churches were. Many of these have been long gone, but if the property is agricultural, and with permission from the land owner, there can be some nice finds made. I look for signs of a pre existing structures such as broken glass and pottery shards, pieces of red brick, and pieces of limestone. It is not uncommon to find coins laying on top of the ground after a rain. I once found a very nice 1876 Seated Liberty quarter that way.
I can usually search these areas early in the season, before the crops are planted, then when the crops are planted, I focus on the construction projects.