Enters Wake County 2 miles south of Fuquay-Varina.
Leaves Wake County 1 mile northeast of intersection with NC 96.

Major
Intersections:

NC 42 and NC 55 in Fuquay-Varina.  For a time, all three roads are multiplexed.
M-US 70 and NC 50 from western Garner to just north of downtown.
I-40/440/US 64 exit 298A-B.
I-440 (again) exit 11A-B.
M-US 1 from I-440 exit 11B to 3 miles north of the interchange.
NC 96 in the middle of nowhere, 10 miles northeast of Raleigh proper.

History:

US 401 is all over the map.  Literally.  On some maps, the southern half of 401 (from Garner south) was marked as such in the mid '30s.  This implies that 401 has existed in Wake County since then.

Or has it?  Those same maps have 401 marked as US 15A just a few years later.  Apparently 401 didn't have many friends at the DOT.

Meanwhile, NC 59 was leading a charmed life in northern Wake County, running all the way to the Virginia border.  But, come 1956, US 401 made a triumphant (?) return to the county, killing 59 in the process.  401 was now not only signed over what was 15A (but apparently was 401 in a former life), but over the former 59.  And it's stayed the same ever since, except for a short time when it was signed on the Beltline in the early '90s.  At one point, 401 (and 59 before it) ran over Kyle Drive in north Raleigh, but the road was rerouted in the mid-'70s to its current alignment.

Comments:

401 was widened to four lanes divided from Garner to Fuquay in 1996-97, and a six-lane widening from the US 1/401 split north to the Neuse River was completed in early 2003. This leaves only the short part south of Fuquay and the distance from the Neuse through Rolesville to Franklin County as the only remaining 2-lane sections of 401 in the county.

The widening of the northern part of 401, which actually will continue north to Louisburg in Franklin County, will contain a bypass to the southeast of Rolesville. This project is scheduled to begin construction in 2008.

The scarecrow at the top of the page was a landmark for more than twenty years on 401 between Spring Forest and Perry Creek roads, on a farm that was located at what's now at the northeast corner of 401 and I-540.  The farm, though, was sold to a developer, and the scarecrow is no more.  (More on the scarecrow in this article from the News and Observer)