which control option some one opt?

Hello Dear:
For less than 1000 IO's scattered within 1km of area for 4 nos utility plants with one one control room, which option one should adopt?

If it is 1 Km then its not too big area , Be specific which type of Control you are asking for,
May be Distributed Control system is what you are asking.
USe Digital and Analogs Junction Box of IP 65 and take all the signal and digital cables to Control Room .
Be specific How many DO,DI,AO,AI,RTD are there then u can easily choose the Type of PLC.

It is way too little information to decide such a critical technology.

It could be that you need a DCS style control system.
In that case Foundation Fieldbus or Profibus PA would be the natural choice.

Or you may need a PLC style control system.
In that case, I would consider Profinet or Ethernet/IP or similar.
And then the ethernet network should be setup in a redundant fiber backbone.