Underclassmen: Who is staying and who is going?

I'd like to know the deadline to declare for the NFL draft. I thought Vic Beasely was coming out last year and he decided to come back at the last minute. In fact, there was a student at Clemson on JI who said "I saw him in class today. He's staying". I stuck to my original source and obviously was mistaken.

Shawn Oakman and Duke WIlliams to return to school in 2015. Really surprised that Oakman is not coming out this year.

CBS Sports CFB ‏@cbssportscfb 6m6 minutes ago
Baylor DE Shawn Oakman said Monday he will return for his senior season cbsprt.co/1xce230 (USATSI)

The Auburn Plainsman ‏@theauplainsman 2m2 minutes ago
Gus Malzahn has announced that Duke Williams will not play in the Outback Bowl, but plans to return to Auburn next season.

List of Underclassmen declaring as of this AM:

www.rotoworld.com/articles/cfb/50910/394/2015-nfl-draft-announcements

Declaring

QB Brett Hundley, UCLA (source)

RB Todd Gurley, Georgia (source)
RB Melvin Gordon III, Wisconsin (source)
RB Mike Davis, South Carolina (source)
RB Jay Ajayi, Boise State (source)
RB Duke Johnson, Miami (source)
RB Tevin Coleman, Indiana (source)
RB Josh Robinson, Miss State (source)
RB Dee Hart, Colorado State (source)
RB Trey Williams, Texas A&M (source)
RB Matt Jones, Florida (source)

WR Devin Funchess, Michigan (source)
WR Jaelen Strong, Arizona State (source)
WR Nelson Agholor, USC (source)
WR Sammie Coates, Auburn (source)
WR Stefon Diggs, Maryland (source)
WR Nigel King, Kansas (source)
WR Shaq Roland, South Carolina (source)

TE Maxx Williams, Minnesota (source)
TE Jesse James, Penn State (source)
TE Tyler Kroft, Rutgers (source)
TE Jean Sifrin, UMass (source)

T Andrus Peat, Stanford (source)
T Jeremiah Poutasi, Utah (source)
T Donovan Smith, Penn State (source)
T Ereck Flowers, Miami (source)
T D.J. Humphries, Florida (source)

G Tyler Moore, Florida (source)

EDGE Randy Gregory, Nebraska (source)
EDGE Dante Fowler Jr., Florida (source)
EDGE Eli Harold, Virginia (source)
EDGE Shane Ray, Missouri (source)
EDGE Danielle Hunter, LSU (source)
EDGE Noah Spence, Ohio State (source)
EDGE Deion Barnes, Penn State (source)

DL Leonard Williams, USC (source)
DL Jordan Phillips, Oklahoma (source)
DL Christian Covington, Rice (source)
DL Xavier Cooper, Washington State (source)

LB Shaq Thompson, Washington (source)
LB Kwon Alexander, LSU (source)

CB Marcus Peters, Washington (source)
CB Alex Carter, Stanford (source)
CB Trae Waynes, Michigan State (source)
CB Jalen Collins, LSU (source)
CB Lorenzo Doss, Tulane (source)

S Durell Eskridge, Syracuse (source)
S Gerod Holliman, Louisville (source)
S James Sample, Louisville (source)

James Sample has declared

Better player than Holliman IMO

Agreed 

A lot of his picks stemmed from him simply being in the right place at the right time.

I wouldn't mind taking him, say, in the 5th round to use as an extra deep safety in obvious 3rd and long passing situations but I have no clue why some have him graded as a high 2nd rounder.

No doubt, Holliman is definitely benefiting from "box score scouting reports".