On reviewing the census and other statistics, connected with the growth and present and prospective condition of the city, there will be found no cause for despondency and discouragement, but much for congratulation and hope. It is true that no such rapid increase of population has taken place as was anticipated, or as has been the case in some other western towns. But there has been no decrease, even temporary. On the contrary, there has been a steady and gradual increase in population, business and wealth, from the recommencement of the work of building the canal in 1843, to the present time. That this increase has been no more rapid, may be accounted for, partially by the influence which the sudden and nearly simultaneous construction of such a net work of rail roads as covers Illinois, exerts upon all interior towns. There are here no mountain barriers to obstruct the construction of a rail road in any direction. With the exception of the Central, they all cross the State from east to west, connecting the Lakes with the Mississippi, and run without much reference to the location of existing towns. The consequence has been, that nearly all the towns upon the river have had their trade temporarily diverted, to a greater or lesser extent; and "prairie towns" have started up, to compete for the trade, at almost every station. These have enjoyed an ephemeral advantage, from their supposed superior healthiness. That this is a mistake, the mortality of Peru, as exhibited by the census table, for one year, 1857,--which is a fair average of every year except those when the cholera prevailed--abundantly shows. That these towns, while they have in no instance wholly stopped the increase of those on the river, but only divided their natural accessions, will shortly react upon their older sisters, and, in their turn, contributed to their advancement and prosperity, is inevitable. This is already manifest in the relation which Peru now occupies in reference to Amboy, Sublette, Mendota, Arlington, Tonica, Wenona, and other towns on the Central, Chicago and Burlington, and Rock Island Rail Roads, none of which had an existence before the roads were projected. That this is, and must continue to be the case, is obvious from the fact, that while she has all the advantages of rail roads which any of them possess, she has in addition the superior facilities which the river and canal afford. That considerable accessions to her population have taken place the present season is proved by the fact, that only fifteen tenements, little and big, are vacant, while over fifty have been erected.--The foreign element in the population, it will be perceived, is quite large. This is the case with all western towns. If, from the number set down in the census tables as "born in the United States," be subtracted the number "born of foreign parents and counted as Americans," there will be left only nine hundred and seventy-two who are Americans by birth and ancestry.