Camp Dennison this morning. The remainder of the regiment will reach here to-morrow and Camp Dennison on Monday. The mustering of the Twelfth and Thirteenth is nearly completed. A working party of 100 from each will go to Camp Dennison on Monday morning, the regiments following on Tuesday morning. The ten regiments of State troops will mostly be in the same camp by the close of the week. I now think it will be advisable, both for efficiency and economy, to remove the First Brigade to Cama Dennisson at an early day. I may replace it by one or two regiments of State troops.

Camp Dennison is situated direction on the Little Miami River and railroad, seventen miles from Cincinnati. There is space for nearly 30,000 men, and the locations is such that they can be moved rapidly to any part of the State, as well as to Cincinnati, to which place there is also an excellent turnpike but twelve miles in length. I have already taken steps to obtain early information of any movements from the south on Cincannati, and hope soon to be in condition to meet it. I would suggest that such an advance can but be met by crossing to the Kentucky side, and would impress upon the general that I am fully aware of the necessity of taking no such step prematurely. I have sent Lieutenant Poe to make a reconnaissance of the southeastern frontier, to obtain information concerning the Virginia side, particularly the valley of the Great Kanawha and Fishing Creek, at the base of the Pan Handle. He is also instructed to ascertain, as far as practicable, the state of feeling of the inhabitants of the Virginai side, and to organize means of obtaining reliable and constant information from that quarter. I have sent about 500 stand of arms belonging to the State and some ammunition to the most exposed and alarmed points of that frontier. I have steadily resisted all application for troops in that direction for the present, not having any regiments armed and disciplined, but having them in position to check any strong attack without delay. I have also felt that it would be politic to avoid any display of force ie frontier until I could learn the policy of the lieutenant-general.

I would beg leave to suggest that, to cover Steubenville, and protect the loyal people of the Pan Handle, the most decisive movement, next to an advance up the Kanawha, would be to occupy the line of Fishing Creek, directly at the base of the Pan Handle. I have every reason to believe this to be a strong position, but shall know all about it in a few days. I learned to-day from a confidential and reliable source that there are at Memphis there steamers, the H. R. W. Hill, Mars, and Ohio Belle, chartered by General Pillow, said to be destined for Cairo. I at once telegraphed Governor Yates, Colonel Prentiss, and the adjutant-general of the Department of the West. I shall send down to-morrow night two secret agents, to endeavor to ascertain the truth of this, and will at once inform you, as well as the commanding officer at Cairo, of the result. I have no reason at the present time to apprehend any immediate danger on the frontier, but am certain that we should be on our guard. I will commence the distribution of arms to the men earlyin the week. No acouterments have yet reached us. I hope by Monday or Tuesday to be able to commence regular reports and returns. I feel the want of a good adjutant-general very much.

I am, sir, very respectfully, your obedient servant,

GEO. B. McCLELLAN,

Major, General, Commanding.

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