The central building in a small US mid-western or western town was the railroad station. The Central business district grew up on a street which paralleled the track, or which was more or less perpendicular to it. Note that in many small US towns, even when the railroad was not oriented with a cardinal direction (e.g., N., S., E., or W), the town as laid out was. A small town will have churches of different flavors, typically one for each 50 to 100 people. The exact associations of the churches will depend upon the area of the country, and who settled it. You will need a post office, one or more general stores, a bank or two, a hardware store, a lumber yard, one or more gas stations, a barber shop, perhaps a photographer, an attorney, a diner or two, and a physician or two, and municipal buildings--a municipal hall, a police station, a fire station, and one or more public works facilities. There will also be one or more fraternal or veterans organzitions: Elks, Eagles, Masons, American Legion, or VFW. A larger community might have a movie theater. There will be one or more schools, depending upon the size of the community. There will be a park or two. A larger community will have a car dealer or two, and there will be business catering to the local producers--farmer's co-ops, agricultural equipment dealers, &c. The larger the community, the more of each of the types of assets it is likely to have. Also, the smaller the community, the older the buildings are apt to be.
Finally, keep the density low. Where a larger community might have dwellings on quarter, third, or half acres, the smallest lot in a smaller community may be a half acre, and there might be only three or four developed a block.
Much can be gleaned from the major map sites, especially those with street view, and satellite imagery, especially if you have some idea of what area of the country you want to model. Further information can be gleaned from photo archive sites operated by local historical societies, and by local, regional, state libraries, and even the Library of Congress, in the US.
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