Thunder is right.. closest thing in the US arsenal would be the SM6 variants like the ERAM.
THADD can certainly take down aircraft as well but that's not the primary purpose like Jeff said. S400 OTOH was designed to take down aircraft.
Sorry Kwaig...I worked on the system and THAAD, while billed and funded for the BMD mission, can and will be used whenever necessary to take down any airborne threat, aircraft, non-ballistic and ballistic missiles.
And THAAD is the only US land-based system that has the range and the capability to do so at significant range.
The original name for THAADS was "Theater High Altitude Air Defense System." It was designed with that role of Theater-wide air defense in mind. Later, after Clinton effectively canceled it and then Bush brought it bask, in order to more easily sell it, the name was changed to "Terminal High Altitude Air Defense System". They did this to push the BMD aspect of it and get it funded as such through Congress. but the inherent design remained.
Usually, THAADS will operate in conjunction with other systems...like PAC-2 and PAC-3..from both of which and others it can cue...but neither of them have the range THAAD has.
In terms of range and overall capability...it is as close to S-400 as anything we have.
All of the Standard missile family (outside of the BMD installations being planned in Europe and elsewhere) are, as you say, sea-based systems. They are effective against all manner of airborne targets.
S-400 was designed as a land-based system to be effective against all manner of air borne targets...and it uses three different missiles to do so. The Russians have also developed a version to place at sea.
PAC-2 is a land based system that has an overall capability against all manners of airborne targets, including ballistic missiles...but its range is far less than S-400.
So...comparing all of these is not exactly an apples to apples thing.
In the end, maximum range is one thing to consider...but "effective" range is the critical one. The US has gone to great pains and cost, to ensure a higher effective rate of intercept for its systems over extreme ranges.
In the end...that is what will count.
The S-400 does not have test history to date...and probably will never advertise their testing like the US does... to prove that it is both very effective and can do it at extreme range. Over the coming years, we will see whether it can do both.